Message-ID: <1124215208.430229a8a9cdd@webmail.rawbw.com>
Date: Tue, 16 Aug 2005 11:00:08 -0700
From: mudfoot@rawbw.com
To: pgsql-performance@postgresql.org
Subject: Re: choosing RAID level for xlogs
References: 
 <4BAFBB6B9CC46F41B2AD7D9F4BBAF785098BDF@vt-pe2550-001.VANTAGE.vantage.com>
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 <4BAFBB6B9CC46F41B2AD7D9F4BBAF785098BDF@vt-pe2550-001.VANTAGE.vantage.com>
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Quoting Anjan Dave <adave@vantage.com>:

> Hi,
> 
>  
> 
> One simple question. For 125 or more checkpoint segments
> (checkpoint_timeout is 600 seconds, shared_buffers are at 21760 or
> 170MB) on a very busy database, what is more suitable, a separate 6 disk
> RAID5 volume, or a RAID10 volume? Databases will be on separate
> spindles. Disks are 36GB 15KRPM, 2Gb Fiber Channel. Performance is
> paramount, but I don't want to use RAID0.
> 

RAID10 -- no question.  xlog activity is overwhelmingly sequential 8KB writes. 
In order for RAID5 to perform a write, the host (or controller) needs to perform
extra calculations for parity.  This turns into latency.  RAID10 does not
perform those extra calculations.

>  
> 
> PG7.4.7 on RHAS 4.0
> 
>  
> 
> I can provide more info if needed.
> 
>  
> 
> Appreciate some recommendations!
> 
>  
> 
> Thanks,
> 
> Anjan
> 
>  
> 
>  
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