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Re: Tyan Thunder MB for postgres server

From: William Yu <wyu(at)talisys(dot)com>
To: pgsql-admin(at)postgresql(dot)org
Subject: Re: Tyan Thunder MB for postgres server
Date: 2004-12-16 13:59:48
Message-ID: cps4f6$2dqq$ (view raw, whole thread or download thread mbox)
Lists: pgsql-admin
Iain wrote:

> As bytepile has it, failure of 1 disk in 0+1 leaves you with just RAID 0 
> so one more failure on the other pair and your data is gone. On the 
> other hand, failure of 1 disk in raid 10 leaves you with a working raid 
> 1 that can sustain a second failure.

What they're saying is in the case of (AsB) m (CsD) -- if A fails, they 
no longer count B as part of the array and no longer part of the 
possible drives that can fail. Sorta like the "no one hears a tree fall, 
did it fall" scenario.

I personally disagree with that theory. B is still part of the array. 
Pop in a new drive and the array is ready to start resync (CsD) --> 
(AsB). You still have a 1/3 chance in surviving another drive failure as 
long as B is the one that dies.

Although now that I think about it, RAID10 is more resillient because 
the odds are survival after 1 failure is 2/3. In the case of (AmB) s 
(CmD), if A fails, you can survive C failing or D failing.

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