[Ocfs2-users] ASM over OCFS2 vs. Standard locally managed tablespaces

[Luis Freitas]

Karim,

  This is one big environment.

  I dont see how ASM over OCFS2 would give easier administration than only ASM or only OCFS2. The only situation I see that is reasonable to use ASM over a cooked filesystem would be when using a NAS device that doesnt support direct block access. Also I dont understand why you say that RAC needs a shared filesystem. When you use ASM you dont need to have a shared filesystem.

   If you go ASM, you will need to install the cluster services on each server that shares a ASM diskgroup, even if it has no RAC databases. The same goes to OCFS2, you will need to install the OCFS2 services on each server that shares a OCFS2 filesystem. If you do both, you will have to install both.

   ASM has some interesting "storage" like features, for example extended clusters and online disk reorganization. You can do some of these with OCFS2. For example, adding a disk. But try to remove a OCFS2 volume with the database online and not disrupt your users. ASM can do that.

   On the other hand ASM is less transparent. You have little control on how the data is layout, and the only tool to manage files is a ftp like client, that you need to use to delete dangling files or if you need to backup something manually. Database backups would usually need to go through RMAN. On OCFS2 you can use standard operating system commands to manage the datafiles. ASM also has no recovery tools, like fsck.

Regards,
Luis

--- On Mon, 2/9/09, Karim Alkhayer <kkhayer at gmail.com> wrote:
From: Karim Alkhayer <kkhayer at gmail.com>
Subject: RE: [Ocfs2-users] ASM over OCFS2 vs. Standard locally managed tablespaces
To: lfreitas34 at yahoo.com, ocfs2-users at oss.oracle.com
Date: Monday, February 9, 2009, 10:47 AM




 
 






We’re using OCFS2 for RAC on top of  SLES9, which we’re
going to upgrade to SLES10. Around 10 TB RAID6 multi disk arrays, 5 databases
on RAC, and 5 single instances standby for the primary site 

   

As there is no AI component in ASM to detect the fast LUNs, and
RAC on SLES requires a shared file system. Therefore, on a set of identical
LUNs, in terms of capacity and speed, ASM should take care of distributing the balance
over LUNs, and OCFS2 is expected to work even better if these LUNs are placed
on several disk groups (arrays) 

   

How would this scenario (ASM over OCFS2) work? What are the cons
and pros? Keep in mind that the goal of such a concept is provide performance
and reliability with  the least possible administration 

   

Appreciate your thoughts 

   

Best regards, 

Karim 

   

   



From:
ocfs2-users-bounces at oss.oracle.com [mailto:ocfs2-users-bounces at oss.oracle.com] On
Behalf Of Luis Freitas

Sent: Monday, February 09, 2009 2:16 PM

To: <ocfs2-users at oss.oracle.com>

Subject: Re: [Ocfs2-users] ASM over OCFS2 vs. Standard locally managed
tablespaces 



   


 
  
  Karim,

  

     I dont see why run ASM over OCFS2. It seems to be a useless
  overhead. Either you run ASM or OCFS2.

  

     Btw, neither ASM nor OCFS2 are smart enough to detect that some
  LUNs are faster than others. ASM expects each diskgroup to be comprised of
  LUNs of similar performance in order for it's load balancing algorithms to
  work. OCFS2, as far as I know doesnt have this type of management built in.

  

  See:

  http://www.oracle.com/technology/products/database/asm/pdf/take%20the%20guesswork%20out%20of%20db%20tuning%2001-06.pdf

  Section: ASM Best practices and principals.

  

     About the performance, ASM is said to have similar performance
  to raw devices in a SAME layout, being tightly integrated to Oracle. OCFS2
  has some overheads that are inherent to a file system, like cache management,
  locking, context switching, so it is likely to use more CPU power than ASM.
  But I dont remember any specific benchmark comparing those. 

  

      Also, keep in mind that when you use a filesystem you are
  using part of the memory for the filesystem cache. When using RAW or ASM you
  would need to allocate this memory to the block buffer in order to compare
  results.

  

  Regards,

  Luis 
  

> Hello All,

>

>

>

> Are there any benchmarks with respect to performance with respect to  

> ASM over OCFS2 vs. standard locally managed tablespaces?

>

> In our environment, data files hosting tables/lobs are stored on a  

> RAID6 disk array with 10K rpm disks, whilst indices are  stored on a  

> different RAID6 disk array with 15K rpm disks.

>

> We’re using oracle managed files for the rollback/undo and temporary 

>  tablespaces.

>

> Would ASM over OCFS2 be smart enough to detect the fast LUNs?

>

>

>

> Appreciate your thoughts.

>

>

>

> Best regards,

>

> Karim

>

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> Ocfs2-users at oss.oracle.com

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