RE: ASM disk sizes

From: <Christopher.Taylor2_at_parallon.net>
Date: Mon, 8 Jul 2013 11:39:29 -0500
Message-ID: <F05D8DF1FB25F44085DB74CB916678E887A2A73C62_at_NADCWPMSGCMS10.hca.corpad.net>



a.) Have had disks differently sized in some diskgroups but this was a short term solution to a space problem and was soon corrected. b.) I don't see similar sizes as a luxury and here's why:

        Typically when you create a logical space allocation on a SAN, the performance characteristics are different depending on the size of that space allocation. Some sans make this automatic, while others (I believe) are manually configured. One of the characteristics that come to mind is cache slots at the SAN layer on hyper volumes. So even though a 100GB space allocation and a 750GB space allocation may touch the same number of physical devices in the SAN, there can be other considerations that are not the same. (I'd be interested to hear what Kevin Closson has to say on this as I may be completely off base here)

Regards,
Chris

-----Original Message-----

From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Herring, David Sent: Monday, July 08, 2013 11:18 AM
To: oracle-l_at_freelists.org
Subject: ASM disk sizes

Folks,

I'm running into a discussion with another DBA on our team concerning differing disk (or LUN, but for the sake of simplicity let's just say "disk") sizes within ASM. Best practices for ASM say to use consistent sizes of disks within a diskgroup and I'm sure many of us have run into situations where there was an inconsistency, the smallest disk filled and suddenly Oracle gave space errors even though there was plenty of space on the larger disks. That's just one example of issues that can arrise.

Back to the discussion, I'm told that:

  1. Having consistent disk sizes is a "luxury"
  2. Many places have inconsistent disk sizes, within diskgroups, and work just fine.

Do many of you currently or in the past worked on dbs where the disks were differently sized within diskgroups for ASM? Do most/any of you see consistent disks within diskgroups as a "luxury" and that instead you accept whatever the SAN team gives you?

Even though I've run into issues concerning space with inconsistently sized disks on 10g and 11g and performed A LOT of detailed tracking of the arb processes doing their rebalance work, I'm being ignored. It's rather frustrating to say the least. In one diskgroup they've got disks of 511 GB, 430 GB, 143 GB, and 122 GB. They're all about 32% used so the best as I can figure is rebalance operations weren't fully performed when disks were added.

Dave Herring

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http://www.freelists.org/webpage/oracle-l Received on Mon Jul 08 2013 - 18:39:29 CEST

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