RAC/ASM/VOTING_DISK interview Q&Answer

 What is ASM?

In Oracle Database 10g/11g there are two types of instances: database and ASM instances. The ASM instance, which is generally named +ASM, is started with the INSTANCE_TYPE=ASM init.ora parameter. This parameter, when set, signals the Oracle initialization routine to start an ASM instance and not a standard database instance. Unlike the standard database instance, the ASM instance contains no physical files; such as logfiles, controlfiles or datafiles, and only requires a few init.ora parameters for startup.

Upon startup, an ASM instance will spawn all the basic background processes, plus some new ones that are specific to the operation of ASM. The STARTUP clauses for ASM instances are similar to those for database instances. For example, RESTRICT prevents database instances from connecting to this ASM instance. NOMOUNT starts up an ASM instance without mounting any disk group. MOUNT option simply mounts all defined diskgroups

For RAC configurations, the ASM SID is +ASMx instance, where x represents the instance number.

 What are the key benefits of ASM?

ASM provides filesystem and volume manager capabilities built into the Oracle database kernel. Withthis capability, ASM simplifies storage management tasks, such as creating/laying out databases and disk space management. Since ASM allows disk management to be done using familiar create/alter/drop SQL statements, DBAs do not need to learn a new skill set or make crucial decisions on provisioning.

The following are some key benefits of ASM:

·        ASM spreads I/O evenly across all available disk drives to prevent hot spots and maximize performance.

·        ASM eliminates the need for over provisioning and maximizes storage resource utilization facilitating database consolidation.

·        Inherent large file support.

·        Performs automatic online redistribution after the incremental addition or removal of storage  capacity.

·        Maintains redundant copies of data to provide high availability, or leverages 3rd party RAID functionality.

·        Supports Oracle Database as well as Oracle Real Application Clusters (RAC).

·        Capable of leveraging 3rd party multipathing technologies.

·        For simplicity and easier migration to ASM, an Oracle database can contain ASM and non-ASM files.

·        Any new files can be created as ASM files whilst existing files can also be migrated to ASM.

·        RMAN commands enable non-ASM managed files to be relocated to an ASM disk group.

·        Enterprise Manager Database Control or Grid Control can be used to manage ASM disk and file activities.

Describe about ASM architecture.

Automatic Storage Management (ASM) instance

Instance that manages the diskgroup metadata

Disk Groups

Logcal grouping of disks
Determines file mirroring options
ASM Disks
LUNs presented to ASM
ASM Files 

 

 Files that are stored in ASM disk groups are called ASM files, this includes database files

Notes:

Many databases can connect as clients to single ASM instances

ASM instance name should only be +ASM only

One diskgroup can serve many databases

 How does database connects to ASM Instance?

The database communicates with ASM instance using the ASMB (umblicus process) process. Once the database obtains the necessary extents from extent map, all database IO going  forward is processed through by the database processes, bypassing ASM. Thus we say ASM is not really in the IO path. So, the question how do we make ASM go faster…..you don’t have to.

What init.ora parameters does a user need to configure for ASM instances?

The default parameter settings work perfectly for ASM. The only parameters needed for 11g ASM:
• PROCESSES*
• ASM_DISKSTRING*
• ASM_DISKGROUPS
• INSTANCE_TYPE

How does the database interact with the ASM instance and how do I make ASM go faster?

ASM is not in the I/O path so ASM does not impede the database file access. Since the RDBMS instance is performing raw I/O, the I/O is as fast as possible.

Do I need to define the RDBMS FILESYSTEMIO_OPTIONS parameter when I use ASM?

No. The RDBMS does I/O directly to the raw disk devices, the FILESYSTEMIO_OPTIONS  parameter is only for filesystems.

Why Oracle recommends two diskgroups?

Oracle recommends two diskgroups to provide a balance of manageability, utilization, and performance.

We have a 16 TB database. I’m curious about the number of disk groups we should use; e.g. 1 large disk group, a couple of disk groups, or otherwise?

For VLDBs you will probably end up with different storage tiers; e.g with some of our large customers they have Tier1 (RAID10 FC), Tier2 (RAID5 FC), Tier3 (SATA), etc. Each one of these is mapped to a diskgroup.

We have a new app and don’t know our access pattern, but assuming mostly sequential access, what size would be a good AU fit?

For 11g ASM/RDBMS it is recommended to use 4MB ASM AU for disk groups. See Metalink Note 810484.1

Would it be better to use BIGFILE tablespaces, or standard tablespaces for ASM?

The use of Bigfile tablespaces has no bearing on ASM (or vice versa). In fact most database object related decisions are transparent to ASM.

What is the best LUN size for ASM?

There is no best size! In most cases the storage team will dictate to you based on their standardized LUN size. The ASM administrator merely has to communicate the ASM Best Practices and application  characteristics to storage folks :
• Need equally sized / performance LUNs
• Minimum of 4 LUNs
• The capacity requirement
• The workload characteristic (random r/w, sequential r/w) & any response time SLA
Using this info , and their standards, the storage folks should build a nice LUN group set for you.

In 11g RAC we want to separate ASM admins from DBAs and create different users and groups. How do we set this up?

For clarification
• Separate Oracle Home for ASM and RDBMS.
• RDBMS instance connects to ASM using OSDBA group of the ASM instance.
Thus, software owner for each RDBMS instance connecting to ASM must be
a member of ASM’s OSDBA group.
• Choose a different OSDBA group for ASM instance (asmdba) than for
RDBMS instance (dba)
• In 11g, ASM administrator has to be member of a separate SYSASM group to
separate ASM Admin and DBAs.

Can my RDBMS and ASM instances run different versions?

Yes. ASM can be at a higher version or at lower version than its client databases. There’s two
components of compatiblity:
Software compatibility
Diskgroup compatibility attributes:
compatible.asm
compatible.rdbms

Where do I run my database listener from; i.e., ASM HOME or DB HOME?

It is recommended to run the listener from the ASM HOME. This is particularly important for RAC env, since the listener is a node-level resource. In this config, you can create additional [user] listeners from the database homes as needed.

How do I backup my ASM instance?

Not applicable! ASM has no files to backup, as its does not contain controlfile,redo logs etc.

When should I use RMAN and when should I use ASMCMD copy?

·        RMAN is the recommended and most complete and flexible method to backup and transport database files in ASM.
ASMCMD copy is good for copying single files
• Supports all Oracle file types
• Can be used to instantiate a Data Guard environment
• Does not update the controlfile
• Does not create OMF files

I’m going to do add disks to my ASM diskgroup, how long will this rebalance take?

·        Rebalance time is heavily driven by the three items:
1) Amount of data currently in the diskgroup
2) IO bandwidth available on the server
3) ASM_POWER_LIMIT or Rebalance Power Level

We are migrating to a new storage array. How do I move my ASM database from storage A to storage B?

Given that the new and old storage are both visible to ASM, simply add the new disks to the ASM disk group and drop the old disks. ASM rebalance will migrate data online.

Note 428681.1 covers how to move OCR/Voting disks to the new storage array

Is it possible to unplug an ASM disk group from one platform and plug into a server on another platform (for example, from Solaris to Linux)?

No. Cross-platform disk group migration not supported. To move datafiles between endian-ness platforms, you need to use XTTS, Datapump or Streams.

How does ASM work with multipathing software?

It works great! Multipathing software is at a layer lower than ASM, and thus is transparent.
You may need to adjust ASM_DISKSTRING to specify only the path to the multipathing pseudo devices.

Is ASM constantly rebalancing to manage “hot spots”?

No…No…Nope!! ASM provides even distribution of extents across all disks in a disk group. Since each disk will equal number of extents, no single disk will be hotter than another. Thus the answer NO, ASM does not dynamically move hot spots, because hot spots simply do not
occur in ASM configurations. Rebalance only occurs on storage configuration changes (e.g. add, drop, or resize disks).

What are the file types that ASM support and keep in disk groups?

Control files
Flashback logs
Data Pump dump sets

Data files
DB SPFILE
Data Guard configuration

Temporary data files
RMAN backup sets
Change tracking bitmaps

Online redo logs
RMAN data file copies
OCR files

Archive logs
Transport data files
ASM SPFILE

List Key benefits of ASM?

·        Stripes files rather than logical volumes

·        Provides redundancy on a file basis

·        Enables online disk reconfiguration and dynamic rebalancing

·        Reduces the time significantly to resynchronize a transient failure by tracking changes while disk is offline

·        Provides adjustable rebalancing speed

·        Is cluster-aware

·        Supports reading from mirrored copy instead of primary copy for extended clusters

·        Is automatically installed as part of the Grid Infrastructure

 What is ASM Striping?

ASM can use variable size data extents to support larger files, reduce memory requirements, and improve performance.

Each data extent resides on an individual disk.

Data extents consist of one or more allocation units.

The data extent size is:

·        Equal to AU for the first 20,000 extents (0–19999)

·        Equal to 4 × AU for the next 20,000 extents (20000–39999)

·        Equal to 16 × AU for extents above 40,000

ASM stripes files using extents with a coarse method for load balancing or a fine method to reduce latency.

·        Coarse-grained striping is always equal to the effective AU size.

·        Fine-grained striping is always equal to 128 KB.

How many ASM Diskgroups can be created under one ASM Instance?

ASM imposes the following limits:

·        63 disk groups in a storage system

·        10,000 ASM disks in a storage system

·        Two-terabyte maximum storage for each ASM disk (non-Exadata)

·        Four-petabyte maximum storage for each ASM disk (Exadata)

·        40-exabyte maximum storage for each storage system

·        1 million files for each disk group

·        ASM file size limits (database limit is 128 TB):

1.     External redundancy maximum file size is 140 PB.

2.     Normal redundancy maximum file size is 42 PB.

3.     High redundancy maximum file size is 15 PB.

What is a diskgroup?

A disk group consists of multiple disks and is the fundamental object that ASM manages. Each disk group contains the metadata that is required for the management of space in the disk group. The ASM instance manages the metadata about the files in a Disk Group in the same way that a file system manages metadata about its files. However, the vast majority of I/O operations do not pass through the ASM instance. In a moment we will look at how file
I/O works with respect to the ASM instance.

Diagram that how database interacts with ASM when a request is to read or open a datafile.

1A. Database issues open of a database file
1B. ASM sends the extent map for the file to database instance. Starting with 11g, the RDBMS only receives first 60 extents the remaining extents in the extent map are paged in on demand, providing a faster open
2A/2B. Database now reads directly from disk
3A.RDBMS foreground initiates a create tablespace for example
3B. ASM does the allocation for its essentially reserving the allocation units
for the file creation
3C. Once allocation phase is done, the extent map is sent to the RDBMS
3D. The RDBMS initialization phase kicks in. In this phase the initializes all
the reserved AUs
3E. If file creation is successful, then the RDBMS commits the file creation

Going forward all I/Os are done by the RDBMS directly.

Can my disks in a diskgroup can be varied size? For example one disk is of 100GB and another disk is of 50GB. If so how does ASM manage the extents?

Yes, disk sizes can be varied, Oracle ASM will manage data efficiently and intelligent by placing the extents proportional to the size of the disk in the disk group, bigger diskgroups have more extents than lesser ones.

31) What is Intelligent Data Placement?

32) What is ASM preferred Mirror read? How does it useful?

33) What is ACFS?

34) What is ADVM?

What is the major difference between 10g and 11g RAC?

Well, there is not much difference between 10g and 11gR (1) RAC.

But there is a significant difference in 11gR2.

Prior to 11gR1(10g) RAC, the following were managed by Oracle CRS

o   Databases

o   Instances

o   Applications

o   Node Monitoring

o   Event Services

o   High Availability

From 11gR2(onwards) its completed HA stack managing and providing the following resources as like the other cluster software like VCS etc.

·        Databases

·        Instances

·        Applications

·        Cluster Management

·        Node Management

·        Event Services

·        High Availability

·        Network Management (provides DNS/GNS/MDNSD services on behalf of other traditional services) and SCAN – Single Access Client Naming method, HAIP

·        Storage Management (with help of ASM and other new ACFS filesystem)

·        Time synchronization (rather depending upon traditional NTP)

·        Removed OS dependent hang checker etc, manages with own additional monitor process

What are Oracle Cluster Components?

Cluster Interconnect (HAIP)

Shared Storage (OCR/Voting Disk)

Clusterware software

What are Oracle RAC Components?

VIP, Node apps etc.

 What are Oracle Kernel Components (nothing but how does Oracle RAC database differs than Normal single instance database in terms of Binaries and process)

Basically Oracle kernel need to switched on with RAC On option when you convert to RAC, that is the difference as it facilitates few RAC bg process like LMON,LCK,LMD,LMS etc.

To turn on RAC
# link the oracle libraries
$ cd $ORACLE_HOME/rdbms/lib
$ make -f ins_rdbms.mk rac_on
# rebuild oracle
$ cd $ORACLE_HOME/bin
$ relink oracle

Oracle RAC is composed of two or more database instances. They are composed of Memory structures and background processes same as the single instance database.Oracle RAC instances use two processes GES(Global Enqueue Service), GCS(Global Cache Service) that enable cache fusion.Oracle RAC instances are composed of following background processes:

ACMS—Atomic Controlfile to Memory Service (ACMS)
GTX0-j—Global Transaction Process
LMON—Global Enqueue Service Monitor
LMD—Global Enqueue Service Daemon
LMS—Global Cache Service Process
LCK0—Instance Enqueue Process
RMSn—Oracle RAC Management Processes (RMSn)
RSMN—Remote Slave Monitor

What is Clusterware?

Software that provides various interfaces and services for a cluster. Typically, this includes capabilities that:

·        Allow the cluster to be managed as a whole

·        Protect the integrity of the cluster

·        Maintain a registry of resources across the cluster

·        Deal with changes to the cluster

·        Provide a common view of resources

What are the background process that exists in 11gr2 and functionality?

Process Name	Functionality
crsd	•The CRS daemon (crsd) manages cluster resources based on configuration information that is stored in Oracle Cluster Registry (OCR) for each resource. This includes start, stop, monitor, and failover operations. The crsd process generates events when the status of a resource changes.
cssd	•Cluster Synchronization Service (CSS): Manages the cluster configuration by controlling which nodes are members of the cluster and by notifying members when a node joins or leaves the cluster. If you are using certified third-party clusterware, then CSS processes interfaces with your clusterware to manage node membership information. CSS has three separate processes: the CSS daemon (ocssd), the CSS Agent (cssdagent), and the CSS Monitor (cssdmonitor). The cssdagent process monitors the cluster and provides input/output fencing. This service formerly was provided by Oracle Process Monitor daemon (oprocd), also known as OraFenceService on Windows. A cssdagent failure results in Oracle Clusterware restarting the node.
diskmon	•Disk Monitor daemon (diskmon): Monitors and performs input/output fencing for Oracle Exadata Storage Server. As Exadata storage can be added to any Oracle RAC node at any point in time, the diskmon daemon is always started when ocssd is started.
evmd	•Event Manager (EVM): Is a background process that publishes Oracle Clusterware events
mdnsd	•Multicast domain name service (mDNS): Allows DNS requests. The mDNS process is a background process on Linux and UNIX, and a service on Windows.
gnsd	•Oracle Grid Naming Service (GNS): Is a gateway between the cluster mDNS and external DNS servers. The GNS process performs name resolution within the cluster.
ons	•Oracle Notification Service (ONS): Is a publish-and-subscribe service for communicating Fast Application Notification (FAN) events
oraagent	•oraagent: Extends clusterware to support Oracle-specific requirements and complex resources. It runs server callout scripts when FAN events occur. This process was known as RACG in Oracle Clusterware 11g Release 1 (11.1).
orarootagent	•Oracle root agent (orarootagent): Is a specialized oraagent process that helps CRSD manage resources owned by root, such as the network, and the Grid virtual IP address
oclskd	•Cluster kill daemon (oclskd): Handles instance/node evictions requests that have been escalated to CSS
gipcd	•Grid IPC daemon (gipcd): Is a helper daemon for the communications infrastructure
ctssd	•Cluster time synchronisation daemon(ctssd) to manage the time syncrhonization between nodes, rather depending on NTP

Under which user or owner the process will start?

Component	Name of the Process	Owner
Oracle High Availability Service	ohasd	init, root
Cluster Ready Service (CRS)	Cluster Ready Services	root
Cluster Synchronization Service (CSS)	ocssd,cssd monitor, cssdagent	grid owner
Event Manager (EVM)	evmd, evmlogger	grid owner
Cluster Time Synchronization Service (CTSS)	octssd	root
Oracle Notification Service (ONS)	ons, eons	grid owner
Oracle Agent	oragent	grid owner
Oracle Root Agent	orarootagent	root
Grid Naming Service (GNS)	gnsd	root
Grid Plug and Play (GPnP)	gpnpd	grid owner
Multicast domain name service (mDNS)	mdnsd	grid owner

What is startup sequence in Oracle 11g RAC? 11g RAC startup sequence?

This is about to understand the startup sequence of Grid Infrastructure daemons and its resources in 11gR2 RAC.

In 11g RAC aka Grid Infrastructure we all know there are additional background daemons and agents, and the Oracle documentation is not so clear nor the other blog.

For example:- I have found below two diagram follow any one of these.

explanation from diagram

OHASD Phase:-

• OHASD (Oracle High Availability Server Daemon) starts Firsts and it will start

OHASD Agent Phase:-

• OHASD Agent starts and in turn this will start

gipcd	Grid interprocess communication daemon, used for monitoring cluster interconnect
mdnsd	Multicast DNS service It resolves DNS requests on behalf of GNS
gns	The Grid Naming Service (GNS), a gateway between DNS and mdnsd, resolves DNS requests
gpnpd	Grid Plug and Play Daemon, Basically a profile similar like OCR contents stored in XML format in $GI_HOME/gpnp/profiles/<peer> etc., this is where used by OCSSD also to read the ASM disk locations to start up with out having ASM to be up, moreover this also provides the plug and play profile where this can be distributed across nodes to cluster
evmd/ evmlogger	Evm service will be provided by evmd daemon, which is a information about events happening in cluster, stop node,start node, start instance etc.

• cssdagent (cluster synchronization service agent), in turn starts

ocssd

Cluster synchronization service daemon which manages node membership in the cluster

If cssd found that ocssd is down, it will reboot the node to protect the data integrity.

• cssdmonitor (cluster synchronization service monitor), replaces oprocd and provides I/O fencing

• OHASD orarootagent starts and in turn starts

crsd.bin	Cluster ready services, which manages high availability of cluster resources , like stopping , starting, failing over etc.
diskmon.bin	disk monitor (diskdaemon monitor) provides I/O fencing for exadata storage
octssd.bin	Cluster synchronization time services , provides Network time protocol services but manages its own rather depending on OS

CRSD Agent Phase:- crsd.bin starts two more agents

crsd orarootagent(Oracle root agent) starts and in turn this will start

gns	Grid interprocess communication daemon, used for monitoring cluster interconnect
gns vip	Multicast DNS service It resolves DNS requests on behalf of GNS
Network	Monitor the additional networks to provide HAIP to cluster interconnects
Scan vip	Monitor the scan vip, if found fail or unreachable failed to other node
Node vip	Monitor the node vip, if found fail or unreachable failed to other node

crsd oraagent(Oracle Agent) starts and in turn it will start (the same functionality in 11gr1 and 10g managed by racgmain and racgimon background process) which is now managed by crs Oracle agent itself.

·

ASM & disk groups	Start & monitor local asm instance
ONS	FAN feature, provides notification to interested client
eONS	FAN feature, provides notification to interested client
SCAN Listener	Start & Monitor scan listener
Node Listener	Start & monitor the node listener (rdbms?)

 As you said Voting & OCR Disk resides in ASM Diskgroups, but as per startup sequence OCSSD starts first before than ASM, how is it possible?

How does OCSSD starts if voting disk & OCR resides in ASM Diskgroups?

You might wonder how CSSD, which is required to start the clustered ASM instance, can be started if voting disks are stored in ASM? This sounds like a chicken-and-egg problem: without access to the voting disks there is no CSS, hence the node cannot join the cluster. But without being part of the cluster, CSSD cannot start the ASM instance. To solve this problem the ASM disk headers have new metadata in 11.2: you can use kfed to read the header of an ASM disk containing a voting disk. The kfdhdb.vfstart and kfdhdb.vfend fields tell CSS where to find the voting file. This does not require the ASM instance to be up. Once the voting disks are located, CSS can access them and joins the cluster.

To resolve this issue, Oracle ASM reserves several blocks at a fixed location for every Oracle ASM disk used for storing the voting disk.As a result , Oracle Clusterware can access the voting disks present in ASM even if the ASM instance is down and CSS can continue to maintain the Oracle cluster even if the ASM instance has failed.The physical location of the voting files in used ASM disks is fixed, i.e. the cluster stack does not rely on a running ASM instance to access the files. The location of the file is visible in the ASM disk header (dumping the file out of ASM with dd is quite easy):

oracle@rac1:~/ [+ASM1] kfed read /dev/sdf | grep -E ‘vfstart|vfend’

kfdhdb.vfstart:                   96 ; 0x0ec: 0x00000060                          <
kfdhdb.vfend:                    128 ; 0x0f0: 0x00000080                         <

 – The voting disk is not striped but put as a whole on ASM Disks

 – In the event that the disk containing the voting disk fails, Oracle ASM will choose another disk on which to store this data.

How does SCAN works?

1.     Client Connected through SCAN name of the cluster (remember all three IP addresses round robin resolves to same Host name (SCAN Name), here in this case our scan name is cluster01-scan.cluster01.example.com

2.     The request reaches to DNS server in your corp and then resolves to one of the node out of three.  a. If GNS (Grid Naming service or domain is configured) that is a subdomain configured in  the DNS entry for to resolve cluster address the request will be handover to GNS (gnsd)

3.     Here in our case assume there is no GNS, now the with the help of SCAN listeners where end points are configured to database listener.

4.     Database Listeners listen the request and then process further.

5.     In case of node addition, Listener 4, client need not to know or need not change any thing from their tns entry (address of 4^th node/instance) as they just using scan IP.

6.     Same case even in the node deletion.

What is GNS?

Grid Naming service is alternative service to DNS , which will act as a sub domain in your DNS but managed by Oracle, with GNS the connection is routed to the cluster IP and manages internally.

What is GPNP?

Grid Plug and Play along with GNS provide dynamic

In previous releases, adding or removing servers in a cluster required extensive manual preparation.

In Oracle Database 11g Release 2, GPnP allows each node to perform the following tasks dynamically:

o   Negotiating appropriate network identities for itself

o   Acquiring additional information from a configuration profile

o   Configuring or reconfiguring itself using profile data, making host names and addresses resolvable on the network

For example a domain should contain

·        –Cluster name: cluster01

·        –Network domain: example.com

·        –GPnP domain: cluster01.example.com

To add a node, simply connect the server to the cluster and allow the cluster to configure the node.

To make it happen, Oracle uses the profile located in $GI_HOME/gpnp/profiles/peer/profile.xml which contains the cluster resources, for example disk locations of ASM. etc.

So this profile will be read local or from the remote machine when plugged into cluster and dynamically added to cluster.

What are the file types that ASM support and keep in disk groups?

Control files	Flashback logs	Data Pump dump sets
Data files	DB SPFILE	Data Guard configuration
Temporary data files	RMAN backup sets	Change tracking bitmaps
Online redo logs	RMAN data file copies	OCR files
Archive logs	Transport data files	ASM SPFILE

List Key benefits of ASM?

·        Stripes files rather than logical volumes

·        Provides redundancy on a file basis

·        Enables online disk reconfiguration and dynamic rebalancing

·        Reduces the time significantly to resynchronize a transient failure by tracking changes while disk is offline

·        Provides adjustable rebalancing speed

·        Is cluster-aware

·        Supports reading from mirrored copy instead of primary copy for extended clusters

·        Is automatically installed as part of the Grid Infrastructure

List some of the background process that used in ASM?

Process	Description
RBAL	Opens all device files as part of discovery and coordinates the rebalance activity
ARBn	One or more slave processes that do the rebalance activity
GMON	Responsible for managing the disk-level activities such as drop or offline and advancing the ASM disk group compatibility
MARK	Marks ASM allocation units as stale when needed
Onnn	One or more ASM slave processes forming a pool of connections to the ASM instance for exchanging messages
PZ9n	One or more parallel slave processes used in fetching data on clustered ASM installation from GV$ views

What is node listener?

In 11gr2 the listeners will run from Grid Infrastructure software home

·        The node listener is a process that helps establish network connections from ASM clients to the ASM instance.

·        Runs by default from the Grid $ORACLE_HOME/bin directory

·        Listens on port 1521 by default

·        Is the same as a database instance listener

·        Is capable of listening for all database instances on the same machine in addition to the ASM instance

·        Can run concurrently with separate database listeners or be replaced by a separate database listener

·        Is named tnslsnr on the Linux platform

What is SCAN listener?

A scan listener is something that additional to node listener which listens the incoming db connection requests from the client which got through the scan IP, it got end points configured to node listener where it routes the db connection requests to particular node listener.

What is the difference between CRSCTL and SRVCTL?

crsctl manages clusterware-related operations:

·        Starting and stopping Oracle Clusterware

·        Enabling and disabling Oracle Clusterware daemons

·        Registering cluster resources

srvctl manages Oracle resource–related operations:

·        Starting and stopping database instances and services

·        Also from 11gR2 manages the cluster resources like network,vip,disks etc

How to control Oracle Clusterware?

To start or stop Oracle Clusterware on a specific node:

# crsctl stop crs

# crsctl start crs

To enable or disable Oracle Clusterware on a specific node:

# crsctl enable crs

# crsctl disable crs

How to check the cluster (all nodes) status?

To check the viability of Cluster Synchronization Services (CSS) across nodes:

$ crsctl check cluster

CRS-4537: Cluster Ready Services is online

CRS-4529: Cluster Synchronization Services is online

CRS-4533: Event Manager is online

How to check the cluster (one node) status?

$ crsctl check crs

CRS-4638: Oracle High Availability Services is online

CRS-4537: Cluster Ready Services is online

CRS-4529: Cluster Synchronization Services is online

CRS-4533: Event Manager is online

How to find Voting Disk location?

•To determine the location of the voting disk:

# crsctl query css votedisk

## STATE File Universal Id File Name Disk group

– —– —————– ———- ———-

1. ONLINE 8c2e45d734c64f8abf9f136990f3daf8 (ASMDISK01) [DATA]

2. ONLINE 99bc153df3b84fb4bf071d916089fd4a (ASMDISK02) [DATA]

3. ONLINE 0b090b6b19154fc1bf5913bc70340921 (ASMDISK03) [DATA]

Located 3 voting disk(s).

How to find Location of OCR?

·        cat /etc/oracle/ocr.loc

ocrconfig_loc=+DATA

local_only=FALSE

·        #OCRCHECK (also about OCR integrity)

What are types of ASM Mirroring?

Disk Group Type	Supported MirroringLevels	Default Mirroring Level
External redundancy	Unprotected (None)	Unprotected (None)
Normal redundancy	Two-wayThree-way Unprotected (None)	Two-way
High redundancy	Three-way	Three-way

What is ASM Striping?

ASM can use variable size data extents to support larger files, reduce memory requirements, and improve performance.

Each data extent resides on an individual disk.

Data extents consist of one or more allocation units.

The data extent size is:

·        Equal to AU for the first 20,000 extents (0–19999)

·        Equal to 4 × AU for the next 20,000 extents (20000–39999)

·        Equal to 16 × AU for extents above 40,000

ASM stripes files using extents with a coarse method for load balancing or a fine method to reduce latency.

·        Coarse-grained striping is always equal to the effective AU size.

·        Fine-grained striping is always equal to 128 KB.

How many ASM Diskgroups can be created under one ASM Instance?

ASM imposes the following limits:

·        63 disk groups in a storage system

·        10,000 ASM disks in a storage system

·        Two-terabyte maximum storage for each ASM disk (non-Exadata)

·        Four-petabyte maximum storage for each ASM disk (Exadata)

·        40-exabyte maximum storage for each storage system

·        1 million files for each disk group

·        ASM file size limits (database limit is 128 TB):

1.     External redundancy maximum file size is 140 PB.

2.     Normal redundancy maximum file size is 42 PB.

3.     High redundancy maximum file size is 15 PB.

How to find the cluster network settings?

To determine the list of interfaces available to the cluster:

$ oifcfg iflist –p -n

To determine the public and private interfaces that have been configured:

$ oifcfg getif

eth0 192.0.2.0 global public

eth1 192.168.1.0 global cluster_interconnect

To determine the Virtual IP (VIP) host name, VIP address, VIP subnet mask, and VIP interface name:

$ srvctl config nodeapps -a

VIP exists.:host01

VIP exists.: /192.0.2.247/192.0.2.247/255.255.255.0/eth0

…

How to change Cluster interconnect in RAC?

On a single node in the cluster, add the new global interface specification:

$ oifcfg setif -global eth2/192.0.2.0:cluster_interconnect

Verify the changes with oifcfg getif and then stop Clusterware on all nodes by running the following command as root on each node:

# oifcfg getif

# crsctl stop crs

Assign the network address to the new network adapters on all nodes using ifconfig:

#ifconfig eth2 192.0.2.15 netmask 255.255.255.0 \ broadcast 192.0.2.255

Remove the former adapter/subnet specification and restart Clusterware:

$ oifcfgdelif -global eth1/192.168.1.0

# crsctl start crs

Managing or Modifying SCAN in Oracle RAC?

To add a SCAN VIP resource:

$ srvctl add scan -n cluster01-scan

To remove Clusterware resources from SCAN VIPs:

$ srvctl remove scan [-f]

To add a SCAN listener resource:

$ srvctl add scan_listener

$ srvctl add scan_listener -p 1521

To remove Clusterware resources from all SCAN listeners:

$ srvctl remove scan_listener [-f]

How to check the node connectivity in Oracle Grid Infrastructure?

$ cluvfy comp nodecon -n all –verbose

Can I stop all nodes in one command? Meaning that stopping whole cluster ?

In 10g its not possible, where in 11g it is possible

[root@pic1]# crsctl start cluster -all
[root@pic2]# crsctl stop cluster –all

What is OLR? Which of the following statements regarding the Oracle Local Registry (OLR) is true?

1.Each cluster node has a local registry for node-specific resources.

2.The OLR should be manually created after installing Grid Infrastructure on each node in the cluster.

3.One of its functions is to facilitate Clusterware startup in situations where the ASM stores the OCR and voting disks.

4.You can check the status of the OLR using ocrcheck.

What is runfixup.sh script in Oracle Clusterware 11g release 2 installation

With Oracle Clusterware 11g release 2, Oracle Universal Installer (OUI) detects when the minimum requirements for an installation are not met, and creates shell scripts, called fixup scripts, to finish incomplete system configuration steps. If OUI detects an incomplete task, then it generates fixup scripts (runfixup.sh). You can run the fixup script after you click the Fix and Check Again Button.

The Fixup script does the following:

If necessary sets kernel parameters to values required for successful installation, including:

·        Shared memory parameters.

·        Open file descriptor and UDP send/receive parameters.

Sets permissions on the Oracle Inventory (central inventory) directory. Reconfigures primary and secondary group memberships for the installation owner, if necessary, for the Oracle Inventory directory and the operating system privileges groups.

·        Sets shell limits if necessary to required values

Update 12-May-2013, Some practical questions added here

1. Viewing Contents in OCR/Voting disks

 There are three possible ways to view the OCR contents.
 a. OCRDUMP (or)
 b. crs_stat -p  (or)
 c. By using strings.
 Voting disk contents are not persistent and are not required to view the contents, because the voting disk contents will be overwritten. if still need to view, strings are used. 

2. Server pools – Read in my blog

3. Verifying Cluster Interconnect

                   
  Cluster interconnects can be verified by:
 i. oifcfg getif
 ii. From AWR Report.
 iii. show parameter cluster_interconnect
 iv. srvctl config network

4. Does scan IP required or we can disable it

     
    SCAN IP can be disabled if not required. However SCAN IP is mandatory during the RAC installation. Enabling/disabling SCAN IP is mostly used in oracle apps environment by the concurrent manager (kind of job scheduler in oracle apps). 
 To disable the SCAN IP,
 i. Do not use SCAN IP at the client end.
 ii. Stop scan listener
       srvctl stop scan_listener
 iii. Stop scan
       srvctl stop scan (this will stop the scan vip's)
 iv. Disable scan and disable scan listener
      srvctl disable scan

5. Migrating to new Diskgroup scenarious

a. Case 1: Migrating disk group from one storage to other with same name 
        1. Consider the disk group is DATA, 
        2. Create new disks in DATA pointing towards the new storage (EMC), 
                  a) Partioning provisioning done by storage and they give you the device name or mapper like /dev/mapper/asakljdlas
        3. Add the new disk to diskgroup DATA
          a) Alter diskgroup data add disk '/dev/mapper/asakljdlas'  
        3. drop the old disks from DATA with which rebalancing is done automatically.  
        If you want you can the rebalance by alter system set asm_power_limit =12 for full throttle.
            alter diskgroup data drop disk 'path to hitachi storage'
            Note: you can get the device name in v$asm_disk in path column.
        4. Request SAN team to detach the old Storage (HITACHI).

b. Case 2: Migrating disk group from one to another with different diskgroup name.
        1) Create the Disk group with new name in the new storage. 
        2) Create the spfile in new diskgroup and change the parameter scope = spfile for control files etc.
        3) Take a control file backup in format +newdiskgroup
        4) Shutdown the db, startup nomount the database
        5) restore the control file from backup (now the control will restore to new diskgroup)
        6) Take the RMAN backup as copy of all the databases with new format. 
               RMAN> backup database as copy format '+newdiskgroup name' ;
        3) RMAN> Switch database to copy. 
        4) Verify dba_data_files,dba_temp_files, v$log that all files are pointing to new diskgroup name.

c. Case 3: Migrating disk group to new storage but no additional diskgroup given
         1) Take the RMAN backup as copy of all the databases with new format and place it in the disk. 
         2) Prepare rename commands from v$log ,v$datafile etc (dynamic queries)
         3) Take a backup of pfile and modify the following referring to new diskgroup name
                  .control_files
  .db_create_file_dest
  .db_create_online_log_dest_1
  .db_create_online_log_dest_2
  .db_recovery_file_des
                          4) stop the database
                          5) Unmount the diskgroup 
                               asmcmd umount ORA_DATA
                          6) use asmcmd renamedg (11gr2 only) command to rename to new diskgroup 
                               renamedg phase=both dgname=ORA_DATA newdgname=NEW_DATA verbose=true  
                 7)  mount the diskgroup
                      asmcmd mount NEW_DATA
                 8) start the database in mount with new pfile taken backup in step 3
                 9) Run the rename file scripts generated at step2
                 9) Add the diskgroup to cluster the cluster (if using rac)
   srvctl modify database -d orcl -p +NEW_FRA/orcl/spfileorcl.ora 
   srvctl modify database -d orcl -a "NEW_DATA" 
   srvctl config database -d orcl   
   srvctl start database -d orcl 
                                        10) Delete the old diskgroup from cluster
                        crsctl delete resource ora.ORA_DATA.dg 
                11) Open the database.

7. Database rename in RAC, what could be the checklist for you?

 a. Take the outputs of all the services that are running on the databases.
 b. set cluster_database=FALSE
 c. Drop all the services associated with the database.
 d. Stop the database
 e. Startup mount
 f. Use nid to change the DB Name. 
    Generic question, If using ASM the usual location for the datafile would be +DATA/datafile/OLDDBNAME/system01.dbf'
    Does NID changes this path too? to reflect the new db name?
    Yes it will, by using proper directory structure it will create a links to original directory structure. +DATA/datafile/NEWDBNAME/system01.dbf'
    this has to be tested,  We dont have test bed, but thanks to Anji who confirmed it will

 g. Change the parameters according to the new database name
 h. Change the password file.
 i. Stop the database.
 j. Mount the database
 k. Open database with Reset logs
 l. Create spfile from pfile.
 m. Add database to the cluster.
 n. Create the services that are dropped in prior to rename.
 o. Bounce the database.

8.How to find the database in which particular service is attached to when you have a large number of databases running in the server, you cannot check one by one manually

Write a shell script to read the database name from oratab and iterate the loop taking inpt as DB name in srvctl to get the result.
#!/bin/ksh
ORACLE_HOME=
PATH=$ORACLE_HOME/bin:$PATH
LD_LIBRARY_PATH=${SAVE_LLP}:${ORACLE_HOME}/lib
export TNS_ADMIN ORACLE_HOME PATH LD_LIBRARY_PATH
for INSTANCE in `cat /etc/oratab|grep -v "^#"|cut -f1 -d: -s`
do
export ORACLE_SID=$INSTANCE
echo `srvctl status service -d $INSTANCE -s $1| grep -i "is running"`
done

9. Difference between OHAS and CRS
OHAS is complete cluster stack which includes some kernel level tasks like managing network,time synchronization, disks etc, where the CRS has the ability to manage the resources like database,listeners,applications, etc With both of this Oracle provides the high availability clustering services rather only affinity to databases.