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Re: config question (external raid, external log?)

To: linux-xfs@xxxxxxxxxxx
Subject: Re: config question (external raid, external log?)
From: Adrian Head <ahead@xxxxxxxxxxxxxx>
Date: Tue, 28 May 2002 23:37:11 +1000
In-reply-to: <3CF32158.D9329832@xxxxxxxxxxxxxxxx>
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On Tue, 28 May 2002 16:19, Simon Matter wrote:
> With software RAID and XFS it is completely different. At least with
> RAID5 it's a must to have external logs and it doesn't hurt if it's on a
> separate RAID1 on the same spindles. 

Its not quite a _must_ but a nice to have.  Just for my own benefit I ran a 
real quick-n-dirty test.  This involved copying data from one server to 
another - not sure the total size (~18G).

Single Disk = 33:20
RAID0 = 29:20
RAID5 = 39:03
* All volumes are standard XFS created by mkfs.xfs /dev/???
** The RAID0 result above is a very bad assumption of what RAID5 would be 
without an internal log.

For my purposes the differences are close enough and the usage of the machine 
dictates that it doesn't matter.  As if I was waiting for that data I'd go 
and get a coffee and it takes longer than 6mins to do that.  Or I'd have to 
go and deal with the other issues :-)

Of course if your needs are different then as shown above very badly - there 
is a performance reason to have an external log volume when using software 
raid5.

-- 
Adrian Head

(Public Key available on request.)


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