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Re: howto preallocate to minimize fragmentation

To: Ying-Hung Chen <ying@xxxxxxxxxxxxxx>
Subject: Re: howto preallocate to minimize fragmentation
From: Eric Sandeen <sandeen@xxxxxxx>
Date: Thu, 22 Sep 2005 09:40:08 -0500
Cc: linux-xfs@xxxxxxxxxxx
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Ying-Hung Chen wrote:
See the xfsctl man page from xfsprogs, specifically XFS_IOC_RESVSP

creating a sparse file will not help with fragmentation, unfortunately.



Hello again,

Thanks for the info, here are more specifics on what we are trying to do:

we have 200GB of harddive and would like to create 90-95 of 'video'
file, each with 2GBs (data will be writting to each file continuesly,
just like a tape). and we are hoping that if can write to the same
physical place all the time, there won't be any fragmentation problem....

we are wondering if there are any xfs parameters we can do (e.g. volumes
groups?) for the above to 'gaurantee' the best layout since we are not
going to create/delete files once created all those Video files, all we
are doing are overwriting files continuesly.

pre-allocation before writing would still be your best bet. If you pre-allocate on a fresh fs before writing, you should get very large extents.

Other things you could try; if you put each file in its own dir, it will tend to go into its own allocation group.

You could make the filesystem with allocation groups sized at 2GB

-Eric


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