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From: Craig Ringer <ringerc@ringerc.id.au>
To: Ogden <lists@darkstatic.com>
Cc: pgsql-performance@postgresql.org, Greg Smith <greg@2ndquadrant.com>
Subject: Re: Raid 5 vs Raid 10 Benchmarks Using bonnie++
Date: Thu, 18 Aug 2011 13:35:56 +0800
Message-ID: <4E4CA4BC.9050908@ringerc.id.au> (raw)
In-Reply-To: <207E881B-73CD-4C31-A863-2C238838C41F@darkstatic.com>
References: <959BD2FA-0312-458B-BD5F-ED358D2C47ED@darkstatic.com>
	<f4e06a7cad34ee9217a3e57fd4eb0e67.squirrel@sq.gransy.com>
	<D89151D3-D2E5-47E3-8B90-4A573DAB5FFA@darkstatic.com>
	<75A85649-2B95-43D5-8404-4776D2E580EC@darkstatic.com>
	<4E4C2FB4.4010409@2ndQuadrant.com>
	<207E881B-73CD-4C31-A863-2C238838C41F@darkstatic.com>

On 18/08/2011 11:48 AM, Ogden wrote:
> Isn't this very dangerous? I have the Dell PERC H700 card - I see that it has 512Mb Cache. Is this the same thing and good enough to switch to nobarrier? Just worried if a sudden power shut down, then data can be lost on this option.
>
>
Yeah, I'm confused by that too. Shouldn't a write barrier flush data to 
persistent storage - in this case, the RAID card's battery backed cache? 
Why would it force a RAID controller cache flush to disk, too?

--
Craig Ringer



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