Writing contigiously to UFS2?

[Oliver Fromme]

Fluffles <etc at fluffles.net> wrote:
 > I've setup a concat of 8 disks for my new NAS, using ataidle to spindown 
 > the disks not needed. This allows me to save power and noise/heat by 
 > running only the drives that are actually in use.
 > 
 > My problem is UFS. UFS2 seems to write to 4 disks, even though all the 
 > data written so far can easily fit on just one disk. What's going on 
 > here? I looked at newfs parameters, but in the past was unable to make 
 > newfs write contigiously. It seems UFS2 always writes to a new cylinder. 
 > Is there any way to force UFS to write contigiously? Or at least limit 
 > the problem?
 > 
 > If i write 400GB to a 4TB volume consisting of 8x 500GB disks, i want 
 > all data to be on the first disk.

You should be able to achieve that by putting a gvirstor
onto your drives, having the physical size of those eight
drives.  Then newfs that gvirstor device.

I haven't used gvirstor myself, but if I understand it
correctly, it should start filling its providers from the
start, and only begin using the next one when the previous
ones are all completely used.  So it should do exactly
what you want.

http://wiki.freebsd.org/gvirstor

Best regards
   Oliver

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