Writing contigiously to UFS2?

Ivan Voras ivoras at freebsd.org
Fri Sep 21 05:51:53 PDT 2007

Stefan Esser wrote:
> Ivan Voras wrote:

>> (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" ;-)

Of course, I mean no disrespect to them, I've read enough papers on them 
to realize their complexity :) By "dumb" I meant they behave like "point 
them to a device and they will stick to it", i.e. they don't come with a 
volume manager.

> 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).

[thinking out loud:]

 From experience (not from reading code or the docs) I conclude that 
cylinder groups cannot be larger than around 190 MB. I know this from 
numerous runnings of newfs and during development of gvirstor which 
interacts with cg in an "interesting" way. I know the reasons why cgs 
exist (mainly to lower latencies from seeking) but with todays drives 
and memory configurations it would sometimes be nice to make them larger 
or in the extreme, make just one cg that covers the entire drive. 
Though, this extreme would in case of concat configurations put all of 
block and inode metadata on the first drive which could have interesting 
effects on performance. Of course, with seek-less drives (solid state) 
there's no reason to have cgs at all.

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