From: Peter T. Breuer <ptb@inv.it.uc3m.es>
To: Matthew Wakeling <matthew@flymine.org>
Cc: pgsql-performance@postgresql.org
Subject: Re: Hardware vs Software RAID
Date: Wed, 25 Jun 2008 15:11:23 +0200 (MET DST)
Message-ID: <200806251311.m5PDBNv23559@inv.it.uc3m.es> (raw)
In-Reply-To: <Pine.LNX.4.64.0806251355090.4085@aragorn.flymine.org>
"Also sprach Matthew Wakeling:"
> >> Has anyone done some benchmarks between hardware RAID vs Linux MD software
> >> RAID?
...
> > The upshot is I don't really see a difference in performance.
>
> The main difference is that you can get hardware RAID with
> battery-backed-up cache, which means small writes will be much quicker
> than software RAID. Postgres does a lot of small writes under some use
It doesn't "mean" that, I'm afraid. You can put the log/bitmap wherever
you want in software raid, including on a battery-backed local ram disk
if you feel so inclined. So there is no intrinsic advantage to be
gained there at all.
> However, not all hardware RAID will have such a battery-backed-up cache,
> and those that do tend to have a hefty price tag.
Whereas software raid and a firewire-attached log device does not.
Peter
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To: pgsql-performance@postgresql.org
Cc: ptb@inv.it.uc3m.es, matthew@flymine.org
Subject: Re: Hardware vs Software RAID
In-Reply-To: <200806251311.m5PDBNv23559@inv.it.uc3m.es>
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