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From: Craig Ringer <craig@postnewspapers.com.au>
To: david@lang.hm
Cc: Gregory Stark <stark@enterprisedb.com>
Cc: Andrej Ricnik-Bay <andrej.groups@gmail.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: What is the best way to storage music files in Postgresql
Date: Wed, 19 Mar 2008 07:52:32 +0900
Message-ID: <47E047B0.3090100@postnewspapers.com.au> (raw)
In-Reply-To: <alpine.DEB.1.00.0803181259540.21250@asgard.lang.hm>
References: <8fb205ea0803152311n2c950758g253f4cefd20cff7d@mail.gmail.com>
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	<8fb205ea0803171139h63b55fdrf62776851583a74d@mail.gmail.com>
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	<alpine.DEB.1.00.0803181104010.21250@asgard.lang.hm>
	<87bq5blsr6.fsf@oxford.xeocode.com>
	<alpine.DEB.1.00.0803181259540.21250@asgard.lang.hm>

david@lang.hm wrote:
> you can? I've never seen a raid 5 setup with more then a single parity 
> dirve (or even the option of having more then one drives worth of 
> redundancy). you can have hot-spare drives, but thats a different thing.
>
With RAID 4, where the "parity drives"  are in fact dedicated to parity 
information, the controller could just store the parity data mirrored on 
more than one drive. Unfortunately write performance on RAID 4 is 
absolutely horrible, and a second or third parity disk would not help 
with that.

I suppose there's nothing stopping a controller adding a second disk's 
worth of duplicate parity information when striping a four or more disk 
RAID 5 array, but I thought that's basically what RAID 6 was.

--
Craig Ringer



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