Writing contigiously to UFS2?

[Stefan Esser]

Ivan Voras wrote:
> Fluffles wrote:
> 
>> Even worse: data is being stored at weird locations, so that my energy
>> efficient NAS project becomes crippled. Even with the first 400GB of
>> data, it's storing that on the first 4 disks in my concat configuration, 
> 
>> In the past when testing geom_raid5 I've tried to tune newfs
>> parameters so that it would write contiguously but still there were
>> regular 2-phase writes which mean data was not written contiguously. I
>> really dislike this behavior.
> 
> I agree, this is my least favorite aspect of UFS (maybe together with
> nonimplementation of extents), for various reasons. I feel it's time to
> start heavy lobbying for finishing FreeBSD's implementations of XFS and
> raiserfs :)
> 
> (ZFS is not the ultimate solution: 1) replacing UFS monoculture with ZFS
> monoculture will sooner or later yield problems, and 2) sometimes a
> "dumb" unix filesystem is preferred to the "smart" ZFS).

Both XFS and ReiserFS are quite complex compared to UFS definitely
not well described by the term "dumb" ;-)

The FFS paper by McKusick et.al describes the historical allocation
strategy, which was somewhat modified in FreeBSD a few years ago in
order to adapt to modern disk sizes (larger cylinder groups, meaning
it is not a good idea to create each new directory in a new cylinder
group).

The code that implements the block layout strategy is easily found
in the sources and can be modified without too much risk to your
file systems consistency ...

Regards, STefan