From: Hannes Dorbath <light@theendofthetunnel.de>
Subject: Arguments Pro/Contra Software Raid
Date: Tue, 09 May 2006 11:16:45 +0200
Organization: Hub.Org Networking Services
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To: pgsql-general@postgresql.org pgsql-performance@postgresql.org

Hi,

I've just had some discussion with colleagues regarding the usage of 
hardware or software raid 1/10 for our linux based database servers.

I myself can't see much reason to spend $500 on high end controller 
cards for a simple Raid 1.

Any arguments pro or contra would be desirable.

 From my experience and what I've read here:

+ Hardware Raids might be a bit easier to manage, if you never spend a 
few hours to learn Software Raid Tools.

+ There are situations in which Software Raids are faster, as CPU power 
has advanced dramatically in the last years and even high end controller 
cards cannot keep up with that.

+ Using SATA drives is always a bit of risk, as some drives are lying 
about whether they are caching or not.

+ Using hardware controllers, the array becomes locked to a particular 
vendor. You can't switch controller vendors as the array meta 
information is stored proprietary. In case the Raid is broken to a level 
the controller can't recover automatically this might complicate manual 
recovery by specialists.

+ Even battery backed controllers can't guarantee that data written to 
the drives is consistent after a power outage, neither that the drive 
does not corrupt something during the involuntary shutdown / power 
irregularities. (This is theoretical as any server will be UPS backed)


-- 
Regards,
Hannes Dorbath