RE: Write cache for a SAN
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.
From: oracle-l-bounce_at_freelists.org on behalf of Svetoslav Gyurov Sent: Mon 11/3/2008 10:17 AM
Cc: oracle-l-freelists; oracle-db-l
Subject: Re: Write cache for a SAN
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.
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
http://www.freelists.org/webpage/oracle-l Received on Mon Nov 03 2008 - 12:25:07 CST