[CentOS-virt] LVM mirror database to ramdisk

Fri Jan 22 23:36:26 UTC 2016
Ed Heron <Ed at Heron-ent.com>

On Fri, 2016-01-22 at 16:59 -0600, NightLightHosts Admin wrote:
> On Fri, Jan 22, 2016 at 4:54 PM, Ed Heron <Ed at heron-ent.com> wrote:
> >   Yes, but it isn't that simple.  One copy of the mirror would be on a
> > physical disk.  The other copy of the mirror would be on RAM disk.
> > Since data in RAM doesn't generally survive reboot, the RAM piece would
> > need to be turned off before shutdown and created on startup.
> >
> >> Is there something about LVM mirroring that can handle disks of
> >> different speeds?
> >
> >   With newer LVM, there appears to be some settings that might help with
> > that a bit.  With this older verion, I'd be hoping that the next
> > available disk would handle each request.  If the physical disk takes
> > longer to deal with the writes, the RAM disk might be the one that is
> > available most of the time.
> >
> >   I'd much prefer a method of pre-filling a 35G cache but I saw a
> > reference to creating a disk mirror in RAM and decided to explore it.
> >
> Can you post the results of your test when you get it working?

  Absolutely, I'll share my real world results.  I'm happy that I'm not
the only person interested in the technique.  I'm a little disappointed
somebody isn't telling me there is a much simpler method of putting my
database in RAM.  The technique is only useful in a situation where the
server has gobs of RAM so it might only apply to a small subset of users
but it might speed up database access.  And since it is being done by
the virtual host, the guest doesn't need to know anything about it.
This keeps guest complexity down.  Also, I don't have as much Windows
knowledge as I have Linux knowledge so it was easier for me to implement
under Linux.