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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 | title: Used space in ZFS pools and filesystems
agents: linux, solaris, freebsd
catalog: os/storage
license: GPL
distribution: check_mk
description:
This check monitors the usage of ZFS filesystems using the output
of the command {zfsget}. This is done in a separate check since
the output of {df} does not show the required metrics when ZFS
is used with quotas.
The check is fully compatible with {df} with respect to its configuration,
output and logic. Please refer to the manual of {df} for details.
ZFS has some specialities when compared with "normal" filesystems. From
the point of view of monitoring the crucial difference is that several
filesystems live together in a common "pool". Each of the filesystems
has its own amount of used space. But they share a common free space.
If you want to compute the {percentage} of used/free space of a filesystem,
you may run into trouble. Let's take the following example:
Lets say we have a pool P of the size 10GB where the filesystems A and B
live. Lets assume that A currently uses 2GB and B uses 7GB. That makes 1GB
left available in the pool. Reporting 20% usage for A would be misleading
in such a case, because you would assume 80% (i.e. 8GB) of free space. But
in fact just 1GB is left free for futher files. For that reason our {zfsget}
check reports the current usage plus the available pool space as total size
of the filesystem. In our example that means that the "size" of A is reported
as 3GB with 2GB used (which makes 66.6%). That way all filesystems will
become critical if the available pool space goes to zero.
Filesystems with a {quota} are handled differently, however. Here the quota
is reported as the total size. If A has a quota of 5GB, we report
2GB out of 5GB used.
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