Comments on: ASM multi-disk performance

By: Christo Kutrovsky

Christo Kutrovsky — Tue, 13 Dec 2011 04:07:38 +0000

I don’t think you should be asking this question on the internet. Rather you should prepare a test case and run it.

If you are to move 900GB over 24 hours, that averages 10 Mb/sec – sounds doable to me.

But entire operation is online, I don’t see the reason for time constraint.

By: Bestin

Bestin — Mon, 05 Dec 2011 14:49:14 +0000

Hi,

We have got a Oracle RAC cluster on HP UX . There is one Database 900 GB on a 1.2TB single LUN. This is on EVA 4100.
We are plannign to move this data by ASM rebalancing. We will connect the new SAN (EVA 6400) with 100GB *15 LUNS. We need to disconnect the OLD SAN EVA 4000. All activity has to be completed in 24 Hours is it possible ?

Thanks
BEstin

By: Christo Kutrovsky

Christo Kutrovsky — Tue, 14 Sep 2010 13:54:26 +0000

Goran, that is true, but other than dbwriter and some direct-path operations, there’s not much that does async IO in Oracle (RMAN/backups excluded)

By: goran

goran — Tue, 14 Sep 2010 12:49:14 +0000

to my knowledge queue depth is not related to the number of sessions but rather to the number of IO requests issued … taking into game ASYNC IO, it can be fahr less than 160 sessions to fill up 5×32 queue depth.

goran

By: Christo Kutrovsky

Christo Kutrovsky — Fri, 13 Aug 2010 20:28:50 +0000

Vijay,

A deeper queue is not necessary an advantage. It really depends on the use case. I wouldn’t go to a 5 LUN setup, if I can have one, for a 5% disk IO improvement in a corner case.

Remember, to fill up 5×32 IOs, you need to have 160 sessions requesting IO at the same time.

By: Christo Kutrovsky

Christo Kutrovsky — Fri, 13 Aug 2010 20:27:14 +0000

Hello Tina,

There is nothing specific to do on the SAN side for ASM.

For the database, it’s best to give dedicated spindles, in order to avoid interference from other databases/applications.

Oracle has great performance accounting tools, but if other applications are touching the same disks, Oracle won’t be able to tell this.

On the flip side, it is very easy to resolve your situation. All you have to do is give them another LUN with the 5 spindles, and ask them to add the new one and drop the old one.

ASM will automatically move the data from the old one to the new one (online) and once finished, you can de-allocate the old lun. I recommend a reboot to ensure all file descriptors are closed.

Whether this will solve your DBA team’s backup timing I cannot say.

There are best practices for ASM, in particular to aligning the partitions on the LUNs. See my other blog posts for details.

By: Tina

Tina — Fri, 13 Aug 2010 20:17:01 +0000

Question: I am the SAN administrator and was forced to give disk to the Oracle team at a time when I was really low on disk. They had a Raid-5 array with 5 disks they were using for a file system. The only disk I had available was a Raid-5 array that had 3 disks. I carved up the disk and presented it, and the Linux admin mounted it as an ASM volume. Now, they are complaining about database backups taking twice as long. I admit that the spindle count is super low — I would never have carved it up with so few spindles. We are trying to work out a strategy to give them back disk Raid-5 with 5 disks. But, my concern is ASM vs. regular file system. Is there any Oracle tuning that needs to take place in order to operate optimally while using ASM disk? I am not sure if our dba’s know how to tune the database, so if you could suggest a couple of links and give me a brief overview, I’d be grateful.

By: Vijay

Vijay — Thu, 12 Aug 2010 09:25:10 +0000

Kutrovsky,

IO also depend on SCSI queue depth & HBA card parameters.

Simple test explample for SCSI IO waits,one LUN with 500Gb,the device is /dev/sda on Lunux & SCSI default queue depth is 32 ,more than 32 requests at any time will be queue.
same 500GB divided into 5 Luns ,SDA SDB SDC SDD SDE then the same disks capable of 32*5 requests at a time.
Tune at both SCSI layer & HBA layer we give better perfomance.

-Vijay

By: Analysis of the Oracle Exadata Storage Server and Database Machine

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By: Max

Max — Tue, 01 Jul 2008 14:36:00 +0000

Chris,
Wanted to clarify few things reg your comment “because ASM does not read in blocks of it?s stripe size”..

when you say ASM is using stripe size of 1MB (default for datafiles etc), doesn’t it issue io requests in multiple of 1MB? What should I see on iostat data? Shouldn’t bps/tps = 1MB for all the requests?

can you please clarify w/ some simple test/examples?

In my AIX environment I see less than 1MB value for a io request size ( i.e. “bps: devided by “tps” from iostat ).

-Max.