SSD caching

Follow the instructions at [1] to enable SSD caching

If the dom0 is running Debian, this requires Jessie. Make sure that you're not running some sort of crazy 9.x version of lvm2.

Setting up caching

Mainly, this involves steps like:

 sudo lvcreate -n xcache -L3.6G lvmssd /dev/mdX
 sudo lvcreate -n xcachemeta -L32M lvmssd /dev/mdX
 sudo lvconvert --type cache-pool --cachemode writeback --poolmetadata lvmssd/xcachemeta lvmssd/xcache
 sudo lvconvert --type cache --cachepool lvmssd/xcache lvm1/x

Note that mdX is the SSD RAID drive

 lvremove /dev/lvm1/xcache