Friday, June 11, 2010

Brief on ASM and SGeRAC

Times and again I was asked by my colleagues and friends  about ASM and SG relation.
With release of Oracle 11gR1 and R2 these queries became more frequent.
So here I tried to put together my understanding of the relation between ASM and SG.
I may not be correct in every point and inference. So please share your comments, queries freely.

There are different perspectives of seeing the change of the role of ASM in Oracle Versions 10gr2,11gr1,11gr2 though y one may not be interested in each or all things
still for better understanding this might help .So I divided this document in following sections:
1. What is ASM?
2. SGeRAC and storage options for Oracle
3. Brief on SGeRAC
4. Serviceguard Extension for RAC Version A.11.19
5. new ASM features introduced in 11gR1
6. new ASM features introduced in 11gR2
7. Conclusion
What is ASM?

ASM is nothing but a replacement of volume manager. It acts as an integrated file system and volume manager, providing the performance of raw devices with the ease of management of a file system.
In an ASM environment, you specify a disk group rather than the traditional data file when creating or modifying a database structure such as a table-space.
ASM then creates and manages the underlying files automatically.
Now, if we try to see ASM from the point of High Availability we first have to consider the “shared storage” phenomena [as this is the heart of any HA setup ]and how this is related to ASM.
SGeRAC and storage options for Oracle
SGeRAC supports a variety of storage options for Oracle RAC.
  1. CFS
  2. CVM
  3. SLVM
  4. ASM over Raw Devices
  5. ASM over SLVM
As the combination (5) above is the only configuration that talks about a mixed stack so we’ll concentrate on that for your interest.
In the combined software stack, SGeRAC provides the following to Oracle Clusterware (OC) and RAC:
· Cluster membership to CSS
· Clustered storage to meet the needs of OC and RAC database instance
Oracle Clusterware manages the following:
· Database and associated resources (database instance, services, VIP, listener, etc…)
· ASM instance, when configured.
Brief on SGeRAC
Here comes the SGeRAC toolkit. This Toolkit is based on the contributed Package Integration Framework. This Toolkit provides a uniform, easy to manage and
intuitive method to coordinate the operation of the combined RAC and SGeRAC software stack across the full range of storage management options supported by SGeRAC.
Below is the architecture for SGeRAC:
image
With Serviceguard Extension for RAC Version A.11.19 :
below is the list of Oracle related supported features:
  1. Support for Oracle 11gR1 RAC with SLVM, ASM, CFS, and CVM
  2. SGeRAC on HP-UX 11i v2 with Serviceguard A.11.19 supports Oracle 11gR1 RAC with
  3. SLVM, ASM over SLVM, CFS 5.0 and CVM 5.0.
  4. SGeRAC on HP-UX 11i v3 with Serviceguard A.11.19 supports Oracle 11gR1 RAC with
  5. SLVM, ASM over SLVM or raw disks/LUNs, and CVM/CFS 5.0 and 5.0.1.
Support for the SGeRAC Toolkit
The SGeRAC Toolkit provides documentation and scripts to simplify the integration of SGeRAC and the Oracle 10gR2/11gR1 RAC stack. It also manages the dependency
between Oracle Clusterware and Oracle RAC instances with a full range of storage management options (CFS, SLVM, CVM, ASM over SLVM).
Support for 8192 Oracle Server Processes for Oracle 9iR2, 10gR2 and 11gR1 RAC .The maximum number of Oracle server processes cmgmsd can handle is 8192. When there are more than 8192 server processes connected to cmgmsd, it will start to reject new requests. Oracle foreground server processes are needed to handle the requests of the Database (DB) client connected to the DB instance.
NOTE: Starting with Oracle 10g, Oracle Clusterware processes register with cmgmsd
while Oracle server processes register with Oracle Clusterware. The maximum number
of Oracle server processes supported is determined by Oracle Clusterware. The
maximum number of processes registered by Oracle Clusterware should not exceed
the maximum supported by cmgmsd.
Prior to now, Serviceguard did not support Oracle single instance failover when using ASM
because ASM kept file descriptors open on ASM disk group members even after the disk groups
had been dismounted. Oracle has released patches which address the ASM descriptor issue and
meets the Serviceguard requirement for supporting ASM.
             The framework for ASM integration with Serviceguard makes use of a Multi-Node Package (MNP) to encapsulate the ASM instance and to have the ASM instance running on all nodes, with one or
more Oracle single instance failover packages dependent on this MNP.
Now let us have a look at the new ASM features introduced in 11gR1:
1. ASM Fast Mirror Resync
2. ASM Rolling Upgrade
3. New SYSASM Privilege and OSASM operating system group for ASM Administration
4. ASM Scalability and Performance Enhancements
5. New ASM Command Line Utility (ASMCMD) Commands and Options
6. Enhancements to ALTER DISKGROUP, CREATE DISKGROUP, and DROP DISKGROUP to manage Automatic Storage Management disk groups
7. New Attributes for Disk Group Compatibility
8. ASM Preferred Read Failure Groups
Now , as such , none of the above enhancements comes specially under HA or mixed-stack that is the stack where SGeRAC and ASM both present but as mentioned already SGeRAC A.11.19 supports these new features [ which Oracle implemented on hp platform].
For 11gR2
Automatic Storage Management and Oracle Clusterware Files: With this release, Oracle Cluster Registry (OCR) and voting disks can be placed on Oracle Automatic Storage Management (Oracle ASM).This feature enables Oracle ASM to provide a unified storage solution, storing all the data for the clusterware and the database, without the need for third-party volume managers or cluster filesystems.For new installations, OCR and voting disk files can be placed either on Oracle ASM, or on a cluster file system or NFS system. Installing Oracle Clusterware files on raw or block devices is no longer supported, unless an existing system is being upgraded.
Oracle ASM Job Role Separation Option with SYSASM :The SYSASM privilege that was introduced in Oracle ASM 11g release 1 (11.1) is now fully separated from the SYSDBA privilege. If you choose to use this optional feature, and designate different operating system groups as the OSASM and the OSDBA groups, then the SYSASM administrative privilege is available only to members of the OSASM group. The SYSASM privilege also can be granted using password authentication on the Oracle ASM instance.
You can designate OPERATOR privileges (a subset of the SYSASM privileges, including starting and stopping ASM) to members of the OSOPER for ASM group.
Providing system privileges for the storage tier using the SYSASM privilege instead of the SYSDBA privilege provides a clearer division of responsibility between Oracle ASM administration and database administration, and helps to prevent different databases using the same storage from accidentally overwriting each other's files.
Conclusion: So we can see that release R2 of Oracle also not bringing any change in terms of mixed HA cluster.
                            Thus for a mixed cluster using 11gr1 or r2 ASM with Service Guard SGeRAC A.11.19 should work fine.




Appendix:
References used:

1. http://docs.hp.com/en/5971/SG-SGeRAC-SMS-EMSSupport.htm
2. http://download.oracle.com/docs/cd/E11882_01/server.112/e10713.pdf
3. http://hporacle.com/CTC/index.asp
4. Oracle Database 11g High Availability ,An Oracle White Paper ,June 2007
5. Oracle® Database Storage Administrator's Guide 11g Release 1 (11.1) B31107-05
6. Best Practices for SGeRAC and Oracle RAC, on HP-UX 11i,March 2009 – hp WP
7. http://www.dbaexpert.com/blog/wp-content/uploads/2009/08/doug-top-10-asm-questions.pdf
8. http://www.orafaq.com/wiki/Oracle_11gR1
9. ASM Technical Best Practices [ID 265633.1]: Metalink Note

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