Re: [PLUG] Reclaiming inodes

[Rich Freeman <r-plug@thefreemanclan.net>]

On Thu, Sep 28, 2017 at 7:45 AM, K.S. Bhaskar <bhaskar@bhaskars.com> wrote:
> Might fstransform to transform the filesystem in place to something else
> (xfs seems to never run out of inodes) be an option?
>

I wouldn't switch filesystems JUST because you've run out of inodes.
Various filesystems have various pros and cons and you should make an
informed decision based on your needs.

xfs does allocate inodes dynamically, while ext2/3/4 have static
allocation.  However, with ext4 you can allocate any number that you
wish at time of filesystem creation.  Depending on how the filesystem
is intended to use, or how its use is expected to change over time,
you might choose either as being better.  There are other filesystems
with their own pros and cons.

It looks like you have a relatively small root filesystem, and these
are prone to inode starvation if you don't explicitly allocate more
than the default ratio.  However, if this is otherwise a typical root
filesystem you're probably going to be fine as long as you re-create
it with more.

On ext4 each inode will cost you 256 bytes of space.  You need one for
every single file/link/etc on the filesystem.

The easiest way to adjust the number of inodes is with the -i option
with mkfs.ext4.  The default on my distro at least is a ratio of 16384
bytes per inode.  If you lower the ratio then you'll get more inodes.
If you raise the ratio you'll get less.  If you lower the ratio all
the way to 256 then you'll end up with a filesystem consisting of
nothing but inodes, so you can store gobs of symlinks but no actual
data (well, setting aside tiny files that can be packed into the
inodes).

4096 isn't a bad ratio for a small filesystem that contains a very
large number of small files, which is common for small root
filesystems.  1/16th of your drive will be used up by inodes though.

You can also allocate an explictit number of inodes with -N.

I'm not saying that xfs is a bad choice.  It might be a better choice
for your situation than ext4, or it might be a worse one.  I have no
idea what you're using this system for, and neither does anybody else
here, so nobody can really say one way or the other.  It does allocate
inodes dynamically so you would probably not have this particular
problem (though on most distros you're still capped at 25% of disk
space use for inodes).  You might have others instead, or not.

-- 
Rich
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