From: Simon Waters <simonw@zynet.net>
Organization: ZyNet Limited
To: pgsql-performance@postgresql.org
Subject: Re: Perc 3 DC
Date: Mon, 24 Nov 2008 15:41:43 +0000
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On Monday 24 November 2008 14:49:17 Glyn Astill wrote:
> --- On Mon, 24/11/08, Steve Clark <sclark@netwolves.com> wrote:
> > > Yeah the battery's on it, that and the 128Mb is
> >
> > really the only reason I thought I'd give it a whirl.
> >
> >
> > Is the battery  functioning? We found that the unit had to
> > be on and charged before write back caching
> > would work.
>
> Yeah the battery is on there, and in the BIOS it says it's "PRESENT" and
> the status is "GOOD".

Sorry I deleted the beginning of this on getting back from a week off.

Writeback is configurable. You can enabled write back caching when the unit is 
not charged if you like. It is offered when you create the array (and can be 
changed later). It is arguably a silly thing to do, but it is an option.

I have some reasonable performance stats for this card assuming you have a 
suitably recent version of the driver software, DELL use to ship with a Linux 
kernel that had a broken driver for this card resulting is very poor 
performance (i.e. substantially slower than software RAID). I have a note 
never to use with Linux before 2.6.22 as the LSI driver bundled had issues, 
DELL themselves shipped (if you asked "why is performance so bad") a Redhat 
kernel with a later driver for the card than the official Linux kernel.

That said a couple of weeks back ours corrupted a volume on replacing a dead 
hard disk, so I'm never touching these cheap and tacky LSI RAID cards ever 
again. It is suppose to just start rebuilding the array when you insert the 
replacement drive, if it doesn't "just work" schedule some down time and 
figure out exactly why, don't (for example) blindly follow the instructions 
in the manual on what to do if it doesn't "just work".