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Re: howto preallocate to minimize fragmentation

To: Ying-Hung Chen <ying@xxxxxxxxxxxxxx>
Subject: Re: howto preallocate to minimize fragmentation
From: Andrew Ho <andrewho@xxxxxxxxxxxxx>
Date: Thu, 22 Sep 2005 11:31:49 -0400
Cc: Eric Sandeen <sandeen@xxxxxxx>, linux-xfs@xxxxxxxxxxx
In-reply-to: <4332C636.9070509@xxxxxxxxxxxxxx>
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Ying-Hung Chen wrote:

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.

does this mean, if I create a 2GB file via dd (not sparse file), when i
'overwrite' to the same file, it will stay there? (same physical place)
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


I just thought of wild idea... since i am creating 90 files, what if i
just create 90 allocation group via -d agcount=90, does this make sense
or it won't work at all?

Thanks,

-Ying


From reading your emails, I don't think that it is the problem of the fragmentation. I understand that we don't need to defragment the filesystem while we are working on the unix/linux. I don't need to deframentation a raid drive, which the size
is 2TB, with XFS filesystem.

I guess while you played your video file, which was 2GB. Your video images were not smoothly shown on the player. It gave you an impression that there was a problem on the filesystem.

I don't know whether your 200GB drive is an ATA, SATA or SCSI drive.
A fast SCSI drive is the best drive for the video stream. If you can stipe several SCSI drives
into a volume, and the performance will be improved.

I hope that I can help you to solve your problem.

Andrew


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