RE: Is my Oracle Server issuing more IO than it can handle
- From: "Amaral, Rui" <Rui.Amaral@xxxxxxxxxxxxxxxx>
- To: 'Harel Safra' <harel.safra@xxxxxxxxx>
- Date: Wed, 8 Dec 2010 10:13:10 -0500
Yes in theory that can be true but it depends on several factors:
1) assuming write-back caches on the array have not been disabled (which in my
opinion they should be)
2) the cache is sized correctly for the i/o load mix
3) block size
4) and is some arrays partitioning of the cache to disks
Even if they are adequately gauged there is still no guarantee that the
performance using cache will be sufficient.
This HP white-paper is an example of an XP10K/12K cache paritioning best
practices that Storage admins go through to try and get the best performance
possible:
http://www.filibeto.org/~aduritz/truetrue/storage/xp1/wp/4AA0-6542ENW.pdf
Rui Amaral
Database Administrator
ITS - SSG
TD Bank Financial Group
220 Bay St., 11th Floor
Toronto, ON, CA, M5K1A2
(bb) (647) 204-9106
-----Original Message-----
From: Harel Safra [mailto:harel.safra@xxxxxxxxx]
Sent: Tuesday, December 07, 2010 4:20 PM
To: Amaral, Rui
Cc: 'Oracle Dba Wannabe'; niall.litchfield@xxxxxxxxx; okh@xxxxxxxxxxxxx;
oracle-l@xxxxxxxxxxxxx
Subject: Re: Is my Oracle Server issuing more IO than it can handle
I'd beg to differ.
On modern SANs writes will be acknowledged to the host system once they're
written to cache (and way before they're written to disk).
On the other hand reads can be completed from cache or from disk, depending on
where the data is.
So, unless you're flooding your SAN's cache, writes to SAN will be quicker than
reads.
Harel Safra
On 07/12/2010 22:33, Amaral, Rui wrote:
> It's a good chance that it's cache coming into play - though that is a very
> big generalization. Reads on a storage subsystem are typically faster because
> it doesn't have to worry about such things as parity whereas writes do (this
> is where you're RAID levels come into play).
>
>
> Rui Amaral
> Database Administrator
> ITS - SSG
> TD Bank Financial Group
> 220 Bay St., 11th Floor
> Toronto, ON, CA, M5K1A2
> (bb) (647) 204-9106
>
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