Storage Cache - WriteThrough or WriteBack

From: Hemant K Chitale <hkchital_at_singnet.com.sg>
Date: Wed, 13 Aug 2003 21:39:23 -0800
Message-ID: <F001.005CA8E0.20030813213923@fatcity.com>

I've begun a debate in my organisation about caches on storage systems.
If an Oracle Database, including Redo Log files, is on RAID1 or RAID1+0 or RAID5 on the storage/SAN and the storage/SAN system provides a cache, should the cache be WriteThrough or WriteBack ?

I prefer WriteThrough -- particularly when the Redo Log files are also on such external storage.

The vendor talks of Mirrored-Caches and Battery-Backed Cache.

In the past year, we've had one instance of the Cache itself failing and the Controller stopping all I/O to the storage and a couple of instances of Cache batteries being low/dead. {Should I/O be allowed to proceed if the Cache Batteries are dead or should the storage automatically switch to WriteThrough ?}

Hemant K Chitale
http://hkchital.tripod.com
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Author: Hemant K Chitale
  INET: hkchital_at_singnet.com.sg

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