Writing contigiously to UFS2?

Ivan Voras ivoras at freebsd.org
Fri Sep 21 03:49:47 PDT 2007

Fluffles wrote:
> 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 

There 4 drives are used in what RAID form? If it's RAID0/stripe, you 
can't avoid data being spread across the drives (since this is the point 
of having RAID0).

> 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 the drives are simply concatenated, then there might be weird 
behaviour in choosing what cylinder groups to allocate for files. UFS 
forces big files to be spread across cylinder groups so that no large 
file fills entire cgs.

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