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Re: What is the best way to storage music files in Postgresql

From: david(at)lang(dot)hm
To: Craig Ringer <craig(at)postnewspapers(dot)com(dot)au>
Cc: Gregory Stark <stark(at)enterprisedb(dot)com>, Andrej Ricnik-Bay <andrej(dot)groups(at)gmail(dot)com>, pgsql-performance(at)postgresql(dot)org
Subject: Re: What is the best way to storage music files in Postgresql
Date: 2008-03-18 23:09:59
Message-ID: alpine.DEB.1.00.0803181606140.21250@asgard.lang.hm (view raw or flat)
Thread:
Lists: pgsql-performance
On Wed, 19 Mar 2008, Craig Ringer wrote:

> david(at)lang(dot)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.

just duplicating the Raid 4 or 5 pairity information will not help you if 
the parity drive is not one of the drives that fail.

raid 6 uses a different pairity algorithm so that any two drives in the 
array can fail with no data loss.

even this isn't completely error proof. I just went through a scare with a 
15 disk array where it reported 3 dead drives after a power outage. one of 
the dead drives ended up being the hot-spare, and another drive that acted 
up worked well enough to let me eventually recover all the data (seek 
errors), but it was a very scary week while I worked through this.

David Lang

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