[CentOS-virt] LVM mirror database to ramdisk

Fri Jan 22 17:02:44 UTC 2016
Ed Heron <Ed at Heron-ent.com>

  I'm still running CentOS 5 with Xen.

  We recently replaced a virtual host system board with an Intel
S1400FP4, so the host went from a 4 core Xeon with 32G RAM to a 6 core
Xeon with 48G RAM, max 96G.  The drives are SSD.

  I was recently asked to move an InterBase server from Windows 7 to
Windows Server.  The database is 30G.

  I'm speculating that if I put the database on a 35G virtual disk and
mirror it to a 35G RAM disk, the speed of database access might improve.

  I use local LVM for my virtual disks with DRBD on top to mirror the
disk to a backup server.

  If I change grub.conf to increase RAM disk size and increase host RAM,
I could create a 35G RAM disk.

  I'd modify rc.local to add
	pvcreate /dev/ramdisk
	vgextend vg /dev/ramdisk
	lvconvert -m 1 --corelog vg/lv_database /dev/ramdisk

  Even with lv_database being 35G, it doesn't take long to activate the

  I haven't decided where to put the commands to turn off the lvm
	lvconvert -m 0 vg/lv_database
	vgreduce vg /dev/ramdisk
	pvremove /dev/ramdisk

  I haven't put this in real world use, yet.

  On it's face, this might speed up database access.  Would we expect it
to speed up database access in real world use?

  Should I document the process so others could know how to do this?  I
realize new documentation for CentOS 5 virtualization would be
considered obsolete before I wrote it but I'm expecting to test CentOS 7
virtualization in the next few months and, when I am comfortable, I'd
upgrade my 18 virtual hosts.  I would update the documentation, at that
time, as well.