UFS2 snapshots on large filesystems

[Oliver Fromme]

Eric Anderson <anderson at centtech.com> wrote:
 > Oliver Fromme wrote:
 > > I just accidentally pulled the wrong power cord ...
 > > So now I can give you first-hand numbers.  :-}
 > > 
 > > This is a 250 Gbyte data disk that has been newfs'ed
 > > with -i 65536, so I get about 4 million inodes:
 > > 
 > >       Filesystem     iused      ifree  %iused
 > >       /dev/ad0s1f  179,049  3,576,789     5%
 > > 
 > > So I still have 95% of free inodes, even though the
 > > filesystem is fairly good filled:
 > > 
 > >       Filesystem     1K-blocks         Used       Avail  Capacity
 > >       /dev/ad0s1f  237,652,238  188,173,074  30,466,986     86%
 > > 
 > > fsck(8) took about 2 minutes, which is acceptable, I
 > > think.  Note that I always disable background fsck
 > > (for me personally, it has more disadvantages than
 > > advantages).
 > > 
 > > This is what fsck(8) reported when the machin came
 > > back up:
 > > 
 > >       /dev/ad0s1f: 179049 files, 94086537 used, 24739582 free
 > >       (26782 frags, 3089100 blocks, 0.0% fragmentation)
 > 
 > 180k inodes seems like a pretty small amount to me.

It's my multimedia disk.  It contains mainly multimedia
files, such as images, audio and video files.

 > Here's some info from some of my filesystems:
 > 
 > # df -i
 > Filesystem      1K-blocks        Used      Avail Capacity  iused     ifree %iused  Mounted on
 > /dev/amrd0s1d     13065232    1109204   10910810     9%      663   1695079    0%   /var
 > /dev/label/vol1 1891668564 1494254268  246080812    86% 68883207 175586551   28%   /vol1
 > /dev/label/vol2 1891959846  924337788  816265272    53% 59129223 185364087   24%   /vol2
 > /dev/label/vol3 1892634994 1275336668  465887528    73% 31080812 213506706   13%   /vol3
 > 
 > Even /var has over 1million.

No.  Your /var has just 663 inodes in use, and it has about
1.7 million unused inodes which is just a waste.

Your other file systems use much more inodes, but they're
also much bigger (2 Tbyte) than mine, and they seem to
contain different kind of data.

 > I think your tests are interesting, 
 > however not very telling of many real-world scenarios.

As mentioned above, my "test" was done on my multimedia
file system with an average file size of roughly 1 Mbyte.
Such file systems are quite real-world.  :-)

On a file system containing exclusively video files, innd
cycle buffers or similarly large files, the inode density
can be reduced even further.  If you have a 2 Tbyte file
system that contains only a few thousand files, then you're
wasting 60 Gbytes for unused inode data.

Of course, if you design a file system for different
purposes, your requirements might be completely different.
A maildir server or squid proxy server definitely requires
a much higher inode density, for example.

Best regards
   Oliver

-- 
Oliver Fromme,  secnetix GmbH & Co. KG, Marktplatz 29, 85567 Grafing
Dienstleistungen mit Schwerpunkt FreeBSD: http://www.secnetix.de/bsd
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