Message-ID: <1126735108.43289d040898d@webmail.rawbw.com>
Date: Wed, 14 Sep 2005 14:58:28 -0700
From: mudfoot@rawbw.com
To: pgsql-performance@postgresql.org
Subject: Re: Battery Backed Cache for RAID
References: <PDEOIIFFBIAABMGNJAGPAELFDOAA.pdarley@kinesis-cem.com>
	<1126722523.27650.6.camel@toonses.gghcwest.com>
	<20050914200324.GB26714@surnet.cl> <43288C67.3000209@tweakers.net>
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Bear in mind you will lose data if the raid controller itself fails (or the
cache memory module).  Many solutions have mirrored cache for this reason.  But
that's more $$, depending on the risks you want to take.

Quoting Arjen van der Meijden <acmmailing@tweakers.net>:

> On 14-9-2005 22:03, Alvaro Herrera wrote:
> > On Wed, Sep 14, 2005 at 11:28:43AM -0700, Jeffrey W. Baker wrote:
> > 
> >>On Wed, 2005-09-14 at 11:25 -0700, Peter Darley wrote:
> >>
> >>Actually the cache will just hold its contents while the power is out.
> >>When the power is restored, the RAID controller will complete the writes
> >>to disk.  If the battery does not last through the outage, the data is
> >>lost.
> > 
> > 
> > Just curious: how long are the batteries supposed to last?
> 
> For the LSI-Logic MegaRaid 320-2e its about 72 hours for the standard 
> 128MB version. Their SATA2-solution offers 32 and 72 hour-options. So I 
> assume its "in the order of days" for most RAID controllers.
> 
> Best regards,
> 
> Arjen van der Meijden
> 
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