Thursday, October 30, 2014

Extending a LVM logical volume with SaltStack

How do you, at once, extend a LVM logical volume on a fleet of identical linux (Centos) servers using SaltStack? Here's how and, thanks to Salt, it only took 5m.

Somebody comes into my office in a hurry: we need to extend the XYZ logical volume on all servers or the new app deployment will choke them! I am pretty sure it will not happen, but this would make for a rather uninteresting post, so I set myself to automate the whole thing.

The environment is VMWare, so someone has manually add a 8GB disk to all servers. After that is done from the salt master I comfortably type:

salt 'wftr[2-9].example.it' cmd.run 'parted -s /dev/sda -- mklabel msdos '
salt 'wftr[2-9].example.it' cmd.run 'parted -s /dev/sda -- mkpart primary 0 -0 '
salt 'wftr[2-9].example.it' cmd.run 'sfdisk -l /dev/sda | grep sda1'
salt 'wftr[2-9].example.it' cmd.run 'parted -s /dev/sda -- set 3 LVM on; pvcreate /dev/sda1'
salt 'wftr[2-9].example.it' cmd.run 'vgextend VolGroup00 /dev/sda1'
salt 'wftr[2-9].example.it' cmd.run 'lvextend -l +100%FREE -r /dev/VolGroup00/LogVol00'

Note that I not actually extending *all* servers, but to make it more interesting only those whose name ends in a number between 2 and 9.

The first command writes an empty partition table on the disk, the second creates a primary partition that fills the whole disk. The third command displays the partition table and should be inspected for errors.
The fourth and fifth change the partition type to LVM and creates a physical volume. With the sixth command the pv is added to a volume group, and the new space on the vg is then allocated the logical volume named LogVol00.
The -r option to lvextend tell LVM to also extend the filesystem (ext3) in the same step.

Check out my other SaltStack-related posts.

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