Re: howto preallocate to minimize fragmentation

[Andrew Ho <andrewho@xxxxxxxxxxxxx>]

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