Skip to main content

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]' 'parted -s /dev/sda -- mklabel msdos '
salt 'wftr[2-9]' 'parted -s /dev/sda -- mkpart primary 0 -0 '
salt 'wftr[2-9]' 'sfdisk -l /dev/sda | grep sda1'
salt 'wftr[2-9]' 'parted -s /dev/sda -- set 3 LVM on; pvcreate /dev/sda1'
salt 'wftr[2-9]' 'vgextend VolGroup00 /dev/sda1'
salt 'wftr[2-9]' '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.


Popular posts from this blog

Indexing Apache access logs with ELK (Elasticsearch+Logstash+Kibana)

Who said that grepping Apache logs has to be boring?

The truth is that, as Enteprise applications move to the browser too, Apache access logs are a gold mine, it does not matter what your role is: developer, support or sysadmin. If you are not mining them you are most likely missing out a ton of information and, probably, making the wrong decisions.
ELK (Elasticsearch, Logstash, Kibana) is a terrific, Open Source stack for visually analyzing Apache (or nginx) logs (but also any other timestamped data).

From 0 to ZFS replication in 5m with syncoid

The ZFS filesystem has many features that once you try them you can never go back. One of the lesser known is probably the support for replicating a zfs filesystem by sending the changes over the network with zfs send/receive.
Technically the filesystem changes don't even need to be sent over a network: you could as well dump them on a removable disk, then receive  from the same removable disk.

A not so short guide to ZFS on Linux

Updated Oct 16 2013: shadow copies, memory settings and links for further learning.
Updated Nov 15 2013: shadow copies example, samba tuning.

Unless you've been living under a rock you should have by now heard many stories about how awesome ZFS is and the many ways it can help with saving your bacon.

The downside is that ZFS is not available (natively) for Linux because the CDDL license under which it is released is incompatible with the GPL. Assuming you are not interested in converting to one of the many Illumos distributions or FreeBSD this guide might serve you as a starting point if you are attracted  by ZFS features but are reluctant to try it out on production systems.

Basically in this post I note down both the tought process and the actual commands for implementing a fileserver for a small office. The fileserver will run as a virtual machine in a large ESXi host and use ZFS as the filesystem for shared data.