RE: Is my Oracle Server issuing more IO than it can handle

From: Taylor, Chris David <>
Date: Tue, 7 Dec 2010 14:37:12 -0600
Message-ID: <>

I don't "think" this is exactly right. One physical disk can handle [realistically - assuming 20ms response time on each disk]:
15K SCSI = 135 IOPS
10K SCSI = 90 IOPS
10K SATA = 50 IOPS

7200RPM SATA = 38 IOPS So, depending on the single physical disk, you're still going to run into the IOPS cap on that disk. Let's say your database is small but is generating enough changes to fill up the cache [assuming I understand the way the cache works in your case], the storage server is going to have to write that information out to that 1 disk at some point and I would assume it is going to write it out faster than 135 IOPS if the changes stored in the cache are changing faster than 135 IOPS.

Am I off base on that?

Chris Taylor
Sr. Oracle DBA
Ingram Barge Company
Nashville, TN 37205
Office: 615-517-3355
Cell: 615-663-1673

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From: [] On Behalf Of Harel Safra Sent: Tuesday, December 07, 2010 1:13 PM To:
Cc: Niall Litchfield;; Subject: Re: Is my Oracle Server issuing more IO than it can handle

This calculation is only true if you work with disk drive directly attached to you servers, and even then when there is no cache in the raid controller. Once you start working with central storage systems things like cache size, i/o distribution and disk sharing start to come into play.

For example, our EMC dMX4 storage has 96GB of cache. If your database is smaller than that (and nothing else uses the cache in this example) you could get very high throughput even with a single physical disk.

Do you know which kind of storage you use? Is you system the only system attached to it?

Harel Safra

On 07/12/2010 20:05, Oracle Dba Wannabe wrote: Do any of you have any thoughts w.r.t to question 1 - whether those calculations can be representative of the disks i may need. thanks

  1. Is there someway from awr that I can determine that the Oracle server is issuing more IO than the storage system can handle for example: Physical reads:



Physical writes:



Phy Reads + Phy Writes = 1372 IOPS
Can I then say that if each disk can do 100 IOPS, that the storage system should at least have 13 Disks? (13x100 IOPS)? Or is that an over simplification?

Received on Tue Dec 07 2010 - 14:37:12 CST

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