Set up LVM SSD cache via shell script

lvcacher.sh

#!/bin/bash -u

# Script to automate the setup and conversion of cache pools in LVM.
# I changed all my busy LVs using it, worked well for me.
# Cache and/or thin pools are supported since RHEL 6.4-ish but it's
# more complex/powerful than i.e. bcache. 
# They might be the best tool for you, or might as well not.

# this is as an example, you need to review the script.
# i've also only done basic tests of the error handlers below.
# they seem sound - but again: just an example.


pvname=sdc
vgname=vgxen
lvname=$1


# verify that the lv path we were told to handle is probably ok
lvpre()
{
  test -b /dev/$vgname/$lvname &&
  LV=$(lvdisplay  /dev/$vgname/$lvname) &&
  echo "$LV" | grep -q "LV Write Access        read/write"  &&
  echo "$LV" | grep -q "LV Status              available"
  return $?
}

# verify that the pv path for the cache is part of the VG
pvpre()
{
  test -b /dev/$pvname &&
  PV=$(pvdisplay /dev/$pvname)
  echo "$PV" | grep -q $vgname &&
  echo "$PV" | grep -q "Allocatable           yes"
  return $?
}

# here you (and I likely will, but might take a year or two) could add a check that verifies the 
# thin daemons and tools are in place.

# here you could add another check that verifies two things I didn't need
# 1) LE size for the meta lv - in my case one LE is 256M so I picked -l1
# 2) Verify free space on the cache SSD

# set up the cache
# -y is not passed automatically, in this case, right now, i think it's good.
# it really just slows you down for a few seconds and lets LVM warn you any way it deems good.
cache_lv()
{
  lvcreate -l 1 -n ${lvname}_meta  \
	/dev/$vgname /dev/$pvname
  lvcreate -L4G -n ${lvname}_cache \
	/dev/$vgname /dev/$pvname
  lvconvert --type cache-pool --cachemode writeback --poolmetadata \
	/dev/$vgname/${lvname}_meta /dev/$vgname/${lvname}_cache
  lvconvert --type cache --cachepool \
	/dev/$vgname/${lvname}_cache /dev/$vgname/$lvname
}

if lvpre && pvpre ; then
  cache_lv
else
  echo "there were some errors"
fi

*were :p

@matya hehe