RE: Questions on ASM best practices

From: Hameed, Amir <Amir.Hameed_at_xerox.com>
Date: Tue, 16 Dec 2014 21:28:28 +0000
Message-ID: <AF02C941134B1A4AB5F61A726D08DCED0E12884F_at_USA7109MB012.na.xerox.net>



Hi Stefan,
I appreciate the feedback. I will poke a bit more on some of your comments to clarify my understanding a bit more.
>> However if you want to safe guard some ASM disk group corruptions as well, you should use two ASM disk groups with one redo log member in each. I got a client who uses storage based replication techniques, one ASM disk group for redo and one redo log member only. So it all depends on your environment and safety / performance requirements.

Do you normally store redo logs in their own ASM disk groups (for example, REDO1 & REDO2) or do you use the DATA and RECO/FRA group to store them? The reason I am asking this is that it seems that Oracle now suggests that 128k stripe size for redo logs is not really required and coarse striping can be used, which is also the default. So, if I am using 1M striping for my DATA and RECO groups, that should also work for my redo logs.

Thanks

-----Original Message-----
From: Stefan Koehler [mailto:contact_at_soocs.de] Sent: Tuesday, December 16, 2014 11:41 AM To: Hameed, Amir; oracle-l_at_freelists.org Subject: Re: Questions on ASM best practices

Hi Amir,
unfortunately the most answers are Oracle-like "it depends".

>> How does this change in ASM? For an externally-managed ASM disk
>> group, should there be multiple ASM redo disk groups with each hosting a redo log group or should one ASM redo disk group with multiple members be sufficient?

One ASM disk group with several members *can* be sufficient, if you are using some storage based replication techniques (e.g. NetApp MetroCluster). However if you want to safe guard some ASM disk group corruptions as well, you should use two ASM disk groups with one redo log member in each. I got a client who uses storage based replication techniques, one ASM disk group for redo and one redo log member only. So it all depends on your environment and safety / performance requirements.

>> What is the best approach to manage multiple databases in ASM? Should
>> each DB have its own set of ASM disk groups or should all databases be placed in the same set of disk groups?

It depends on your backup solution (e.g. storage based snapshots) and your will to consolidate and share the disk space. The latter is extremely useful, if you have disk offcuts with file systems and want to get the rid of it. However with the first approach (1 DB = 1 ASM disk group) you may run into some ASM limits now or later ( http://docs.oracle.com/database/121/OSTMG/asmdiskgrps007.htm#OSTMG94136 ), but maybe necessary for dedicated database (storage) snapshots.

>> AU and stripe sizes – For an Oracle E-Business Suite type system, which is hybrid in nature, should the AU size be 1M for the DATA and REDO groups?
>> Should the stripe size be 1M and 128k for DATA and REDO groups respectively?

Based on the Oracle best practices the AU size should be 4 MB (or better said you should set your AU size to the largest I/O that you wish to issue for sequential access). From my performance measurements (mostly with enterprise storage) in client environments the fine-grained striping works better for redo log files (be aware that the default was changed and is coarse nowadays for redo log files) - the data files are usually coarse-grained striped. You should validate this with some generic I/O tests for your (storage) environment when implementing. Oracle also uses variable size extents ( http://docs.oracle.com/cd/E11882_01/server.112/e18951/asmcon.htm#BABCGDBF ). Be also aware that the AU size is used by the free extent search algorithm with LMTs (+ AUTOALLOCATE) and can result in some unexpected behavior ( http://oracle-randolf.blogspot.de/2013/04/asm-au-size-and-lmt-autoallocate.html )

Some ASM best practices are mentioned in this Oracle presentation as well: http://www.dbaexpert.com/blog/wp-content/uploads/2009/08/doug-top-10-asm-questions.pdf

I think so far so good for the start.

Best Regards
Stefan Koehler

Oracle performance consultant and researcher Homepage: http://www.soocs.de
Twitter: _at_OracleSK

> "Hameed, Amir" <Amir.Hameed_at_xerox.com<mailto:Amir.Hameed_at_xerox.com>> hat am 16. Dezember 2014 um 16:17 geschrieben:
>
>
> Hi folks,
>
> I am in the process of implementing ASM for the first time. I have a
> few questions that I would like to ask regarding ASM best practices for both single instance and RAC databases. The Grid/ASM version is 12.1.0.2:
>
> · Redo log file placement – In the non-ASM world, I am used to using two groups for redo logs on multiple mount points with multiple log
> members in each group. How does this change in ASM? For an
> externally-managed ASM disk group, should there be multiple ASM redo disk groups with each hosting a redo log group or should one ASM redo disk group with multiple members be sufficient?
>
> · Managing multiple databases – In the non-ASM world, we allocate a separate set of mount points for each database that we set up. This
> isolates an environment at the storage level and also enables us to
> take storage-based snapshots of a database file systems for backup.
> Restore is also simple and quick where we restore from the online snaps. What is the best approach to manage multiple databases in ASM? Should each DB have its own set of ASM disk groups or should all databases be placed in the same set of disk groups? For example, for databases with SIDs ABCD, MNOP & WXYZ:
>
> o Should there be only one set of ASM disk group (DATA, REDO, RECO, etc.) for all of the above databases OR
>
> o Should ABCD be in its own set of disk group (DATA_ABCD, REDO_ABCD, RECO_ABCO), WXYZ be in its set of disk group (DATA_WXYZ, REDO_ WXYZ,
> RECO_ WXYZ), etc.? This model seems to give more flexibility in terms
> of retiring an environment where a DG could just be dropped and a new one created when setting up a new environment, either via cloning or creating one from scratch.
>
> · AU and stripe sizes – For an Oracle E-Business Suite type system, which is hybrid in nature, should the AU size be 1M for the DATA and
> REDO groups? Should the stripe size be 1M and 128k for DATA and REDO groups respectively?
>
>
>
> Any feedback will be appreciated.
>
>
>
> Thanks,
>
> Amir
>

--
http://www.freelists.org/webpage/oracle-l
Received on Tue Dec 16 2014 - 22:28:28 CET

Original text of this message