Random LVM stuff

LV caching

We use LV caching at least on godard.d.o and smit.d.o. Here are the setup instructions:

• Make sure that both the HDD and SSD are in the same volume group.

• Make sure module loading is enabled

• Run the following command to enable LV caching for the srv LV in the vg0 VG, assuming the SSD is /dev/sda3:

  lvcreate --type cache --cachemode writethrough -L 120G -n srv_cachepool vg0/srv /dev/sda3

• It is currently not possible to resize an LV with a LVM cache. The workaround is to disable LV caching, resize the LV and reenable it. LV caching can be disabled with the following command:

  lvconvert --uncache vg0/srv