RE: Write cache for a SAN
- From: "Matthew Zito" <mzito@xxxxxxxxxxx>
- To: <softice@xxxxxxxxx>, <JBECKSTROM@xxxxxxxxx>
- Date: Mon, 3 Nov 2008 13:25:07 -0500
In agreement, just about every RAID array out there has battery backup on the
cache, or in more advanced arrays, cache with enough battery to stage cache to
at least two disk before shutdown. Even the cruddy built-in RAID cards in
servers today have this. There is very little reason to disable write cache
these days.
Matt
-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx on behalf of Svetoslav Gyurov
Sent: Mon 11/3/2008 10:17 AM
To: JBECKSTROM@xxxxxxxxx
Cc: oracle-l-freelists; oracle-db-l
Subject: Re: Write cache for a SAN
Hi,
No we do not disable it, in particular depending of the model, the EVA
(Enterprise Virtual Array, which is mid-range storage from HP) has two
controllers, each has a 1, 2 or 4 Gb cache which is shared between policy,
read, write and mirror cache. Each controller has hot plug cache batteries (1
or 2, depends on the model) to maintain cache contents for up to 96 hours in
case of a total power failure and/or inappropriate shutdown. After this time
(maybe less) the information in the cache is lost and virtual disks are marked
as broken because they are no more consistent.
--
sve
Jeffrey Beckstrom wrote:
For those of you using a SAN, do you disable the write cache? I am
concerned that if the UPS loses power thus bringing the SAN down,that writes to
the datafiles would be lost. Oracle would think they are completed but never
actually done.
Jeffrey Beckstrom
Database Administrator
Greater Cleveland Regional Transit Authority
1240 W. 6th Street
Cleveland, Ohio 44113
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