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Re: [ADMIN] H/W RAID 5 on slower disks versus no raid on

From: "scott(dot)marlowe" <scott(dot)marlowe(at)ihs(dot)com>
To: "Rajesh Kumar Mallah(dot)" <mallah(at)trade-india(dot)com>
Cc: Steve Crawford <scrawford(at)pinpointresearch(dot)com>,<pgsql-performance(at)postgresql(dot)org>
Subject: Re: [ADMIN] H/W RAID 5 on slower disks versus no raid on
Date: 2002-11-21 19:39:09
Message-ID: Pine.LNX.4.33.0211211235280.23530-100000@css120.ihs.com (view raw or flat)
Thread:
Lists: pgsql-adminpgsql-performance
On Fri, 22 Nov 2002, Rajesh Kumar Mallah. wrote:

> 
> 
> Thanks Steve,
> 
> recently i have come to know that i can only get 3*18 GB ultra160 10K
> hraddrives,
> 
> my OS is lunux , other parameters are
> RAM:2GB , CPU:2*2Ghz Xeon,
> 
> i feel i will do away with raid use one disk for the OS 
> and pg_dumps
> 
> , one for tables and last one for WAL , does this sound good?

That depends.  Are you going to be mostly reading, mostly updating, or an 
even mix of both?

If you are going to be 95% reading, then don't bother moving WAL to 
another drive, install the OS on the first 2 or 3 gigs of each drive, then 
make a RAID5 out of what's left over and put everything on that.  

If you're going to be mostly updating, then yes, your setup is a pretty 
good choice.  

If it will be mostly mixed, look at using a software RAID1.

More important will be tuning your database once it's up, i.e. increasing 
shared buffers, setting random page costs to reflect what percentage of 
your dataset is likely to be cached (the closer you come to caching your 
whole dataset, the closer random page cost approaches 1)




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