check-mk-server 1.2.6p12-1 / usr / share / check_mk / checks-man / zfsget

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.