UFS2 snapshots on large filesystems

[Oliver Fromme]

user <user at dhp.com> wrote:
 > On Sun, 6 Nov 2005, Eric Anderson wrote:
 > > [fsck on large file systems taking a long time]
 > 
 > Can you elaborate ?  Namely, how long on the 2GB filesystems ?

It depends very much on the file system parameters.  In
particular, it's well worth to lower the inode density
(i.e. increase the -i number argument to newfs) if you
can afford it, i.e. if you expect to have fewer large
files on the file system (such as multimedia files).

On a 250 Gbyte drive of mine, I used newfs with -i 131072.
That still leaves enough inodes for about 2 million files,
but reduces fsck time significantly.  A nice side effect
is that it gives you more free space for files, because
every inode occupies 256 bytes in UFS2.  In this case you
I got about 7 Gbyte additional space.

 > As far as the fsck is concerned, this only happens on an ungraceful
 > reboot, right ?

Right.  On a kernel panic, hardware freeze, power failure
or similar things.

 > Assuming a snapshot on a 2GB FS, and assuming no crashes,
 > no long-wait processes like fsck will ever occur, right ?

Right.  But creating the snapshot in the first place takes
a it of time, depending on the size of the file system.

 > Any other comments ?  Do you experience instability/crashes often on
 > systems of this nature ?

No.  I recommend you use 6.0-Release or RELENG_6 (6-stable).

Best regards
   Oliver

-- 
Oliver Fromme,  secnetix GmbH & Co. KG, Marktplatz 29, 85567 Grafing
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