Writing contigiously to UFS2?

Fluffles etc at fluffles.net
Thu Sep 20 16:46:50 PDT 2007

Hello list,

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. If the data spreads, then more disks 
will be 'awaken' when i read my data, which defeats the purpose of my 
power-saving NAS experiment.

Any feedback is welcome. Using FreeBSD 6.2-RELEASE i386, used newfs -U 
-S 2048 <device>.

- Veronica

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