UFS2 snapshots on large filesystems

[Eric Anderson]

Oliver Fromme wrote:
> 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.

Oops!  Thanks for the correction - I misread it in my pasting frenzy. :) 
   It may be a waste, but perhaps the right answer would be in the form 
of a patch to make sysinstall create /var partitions with different 
settings, if you feel strongly about it.  Me personally, in this case, I 
don't care about the space I lose here, since to me it is negligable.


> 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.

Right, this is typical for the types of data I store, which often 
average 8-16k per file, which I think is the default expectation for 
UFS2 filesystems, so I'm making a generalization that a majority of 
users also have a ~16k average filesize.

>  > 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.

True - agreed, however I'm assuming most users of FreeBSD's UFS2 
filesystem are in the 16k average filesize range.   If the average 
users' average file size is larger, than the default newfs parameters 
should be changed, I just don't have any data or research to support 
that, so I'm not certain.

> 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.

If a filesystem were to be designed from scratch, having the inode 
density variable or automatically grow to fulfill the needs, would be 
the most efficient probably.

Eric



-- 
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Eric Anderson        Sr. Systems Administrator        Centaur Technology
Anything that works is better than anything that doesn't.
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