ganglia/gmond_python_modules — pull request #58 by jimjcollins (2012-03-05 16:23:41+00:00)
Title: Added support for recording storage metrics using persistent (across reboots) and meaningful device mapper alias names

These changes add support for capturing metrics via the device mapper alias names as are present in /dev/mapper/ directory when device mapper is in use. This is advantageous for the following reasons:

* In a SAN environment, the device mapper alias names are persistent over reboot in regards to the collection of LUNs which are being measured via that name versus raw scsi device names (/dev/sd*) which are not. Looking at individual device utilization over a time frame which includes a reboot of the host will give meaningful results when the device mapper names are utilized but may not when raw scsi device names are used as you may be comparing data for two different LUNs when utilizing the raw scsi device name.

* If the device mapper aliases are in use with device mapper and LVM, the name of the device for which the metric is being capture is far more recognizable and useful as it typically corresponds a name of a mounted volume. Whereas individual raw scsi devices may be difficult to map to the actual mounted volume they are part of. For instance:

jcollins@db:~> ls -l /dev/mapper/db-d2p1
brw-rw---- 1 root disk 253, 16 Feb 26 02:04 /dev/mapper/db-d2p1
jcollins@db:~> df -h /d2
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/db-d2p1 2.4T 939G 1.5T 40% /d2

where /dev/mapper/db1-d2p1 is a collection of a number of scsi devices whose names don't yield which mounted volume they are associated with nor maintain persistence re the underlying SAN LUNs they represent.