[CentOS-virt] LVM mirror database to ramdisk

Fri Jan 22 20:56:03 UTC 2016
NightLightHosts Admin <admin at nightlighthosts.com>

On Fri, Jan 22, 2016 at 11:02 AM, Ed Heron <Ed at heron-ent.com> wrote:
>   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
> mirror.
>   I haven't decided where to put the commands to turn off the lvm
> mirror.
>         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.

I may not understand enough to understand what you are doing, you want
to actively mirror this with LVM or?