Check MK Plugin to check the health of btrfs filesystems

Informations about BTRFS

How BTRFS works

The BTRFS filesystem stores data in a internal structure called block groups. More informations could be found in the manpage: man mkfs.btrfs -> section BLOCK GROUPS, CHUNKS, RAID.

From the manpage: -- A typical size of metadata block group is 256MiB (filesystem smaller than 50GiB) and 1GiB (larger than 50GiB), for data it’s 1GiB. The system block group size is a few megabytes. -- The command 'btrfs filesystem usage ' displays the allocated sizes. As long as 'Device unallocated' are greater than 1GB new block groups can be always allocated and there is no problem.

But There are some situations that are cirtical:

1. No 'Device unallocated' space is avaliable (or less than 1GB) AND Metadata is running out of space
2. No 'Device unallocated' space is avaliable (or less than 1GB) AND System is running out of space

If no 'Device unallocated' space is avaliable two fixes availiable: "

• extend the disk "
• OR man btrfs-balance --> See examples for parameter -dusage or -musage "

Recommendations

• Run btrfs scrub at least weekly: See tools/btrfs_check.sh for a simple script that scrubs every volume on an server
• For every volume the 'Device unallocated' and METADATA allocation levels should be examined.

Installation

On the Monitoring Server where Check_mk is installed:

For a detailed description how to work with mkp's goto https://docs.checkmk.com/latest/de/mkps.html.

Short tasks

1. copy the XXXXXX.mkp (see dist folder) to your Check_mk server into the /tmp folder.
2. su - <SITE_NAME> (mkp has to be installed on every site you are running!)
3. mkp install /tmp/XXXXXX.mkp (replace XXXXXX with the filename downloaded)
4. Check if installation worked

OMD[mmlan]:~$ find . -iname 'btrfs_health*.py'
./local/share/check_mk/web/plugins/perfometer/btrfs_health.py
./local/share/check_mk/web/plugins/metrics/btrfs_health_metric.py
./local/share/check_mk/web/plugins/wato/btrfs_health.py
./local/lib/python3/cmk/base/plugins/agent_based/btrfs_health.py
...

5. Goto your Check_mk webinterface. Open "Service Rules" and search for BTRFS. BTRFS Health items should appear.

When using the Enterprise Edition

1. Using the WATO's rule search, search for btrfs_health & create a rule of type BTRFS health (Linux) in the Agent plugins section. Enable the distribution of the plugin.
2. Bake new agents in the bakery.
3. On the Linux Server with the btrfs filesystem update the agent with cmk-update-agent -v.

When using the Raw Edition

On the Linux Server with the btrfs filesystem (NOT THE CHECK_MK SERVER!), do the following:

1. Copy the plugin script src/local/share/check_mk/agents/plugins/btrfs_health into /usr/lib/check_mk_agent/plugins/
2. chmod 755 /usr/lib/check_mk_agent/plugins/btrfs_health

Testing the agent plugin

On the Linux Server with the btrfs filesystem execute the script: /usr/lib/check_mk_agent/plugins/btrfs_health. If everythings works the output should look like:

<<<btrfs_health_dstats>>>
btrfs-progs v4.20.1
stats::/bkp/bkp01 [/dev/sdb].write_io_errs    0
stats::/bkp/bkp01 [/dev/sdb].read_io_errs     0
stats::/bkp/bkp01 [/dev/sdb].flush_io_errs    0
stats::/bkp/bkp01 [/dev/sdb].corruption_errs  0
stats::/bkp/bkp01 [/dev/sdb].generation_errs  0
<<<btrfs_health_usage>>>
btrfs-progs v4.20.1
usage::/bkp/bkp01 Overall:
usage::/bkp/bkp01     Device size:                   1288490188800
usage::/bkp/bkp01     Device allocated:              1285297274880
usage::/bkp/bkp01     Device unallocated:                       3192913920
usage::/bkp/bkp01     Device missing:                            0
usage::/bkp/bkp01     Used:                          1129520091136
usage::/bkp/bkp01     Free (estimated):               153920942080      (min: 152324485120)
usage::/bkp/bkp01     Data ratio:                                     1.00
usage::/bkp/bkp01     Metadata ratio:                         2.00
usage::/bkp/bkp01     Global reserve:                    536870912      (used: 0)
usage::/bkp/bkp01
usage::/bkp/bkp01 Data,single: Size:1276640231424, Used:1125912203264
usage::/bkp/bkp01    /dev/sdb   1276640231424
usage::/bkp/bkp01
usage::/bkp/bkp01 Metadata,DUP: Size:4294967296, Used:1803796480
usage::/bkp/bkp01    /dev/sdb   8589934592
usage::/bkp/bkp01
usage::/bkp/bkp01 System,DUP: Size:33554432, Used:147456
usage::/bkp/bkp01    /dev/sdb     67108864
usage::/bkp/bkp01
usage::/bkp/bkp01 Unallocated:
usage::/bkp/bkp01    /dev/sdb   3192913920
<<<btrfs_health_scrub>>>
btrfs-progs v4.20.1
scrub::/bkp/bkp01 scrub status for 253728d8-e806-437d-acc1-1456aaf79e91
scrub::/bkp/bkp01       scrub started at Mon Oct  3 08:06:03 2022 and finished after 06:04:01
scrub::/bkp/bkp01       total bytes scrubbed: 1.06TiB with 0 errors

Services screenshot