Multi-machine mirroring choices

[Sven Willenberger]

On Tue, 2008-07-15 at 16:20 +0100, Pete French wrote:
> > However, I must ask you this: why are you doing things the way you are?
> > Why are you using the equivalent of RAID 1 but for entire computers?  Is
> > there some reason you aren't using a filer (e.g. NetApp) for your data,
> > thus keeping it centralised?
> 
> I am not the roiginal poster, but I am doing something very similar and
> can answer that question for you. Some people get paranoid about the
> whole "single point of failure" thing. I originally suggestted that we buy
> a filer and have identical servers so if one breaks we connect the other
> to the filer, but the response I got was "what if the filer breaks?". So
> in the end I had to show we have duplicate independent machines, with the
> data kept symetrical on them at all times.
> 
> It does actually work quite nicely actually - I have an "'active" database
> machine, and a "passive". The opassive is only used if the active fails,
> and the drives are run as a gmirror pair with the remote one being mounted
> using ggated. It also means I can flip from active to passive when I want
> to do an OS upgrade on the active machine. Switching takes a few seconds,
> and this is fine for our setup.
> 
> So the answer is that the descisiuon was taken out of my hands - but this
> is not uncommon, and as a roll-your-own cluster it works very nicely.
> 
> -pete.
> _______________________________________________

I have for now gone with using ggate[cd] along with zpool and so far
it's not bad. I can fail the master, stop ggated on the slave at which
point geom reads the glabeled disks. From there I can zpool import to an
alternate root. When the master comes back up I can zpool export and
then, on the master, zpool import at which point zfs handles the
resilvering.

The *big* issue I have right now is dealing with the slave machine going
down. Once the master no longer has a connection to the ggated devices,
all processes trying to use the device hang in D status. I have tried
pkill'ing ggatec to no avail and ggatec destroy returns a message of
gctl being busy. Trying to ggatec destroy -f panics the machine.

Does anyone know how to successfully time out a failed ggatec connection
so that I can zpool detach or somehow have zfs removed the unavailable
drive?

Sven
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 189 bytes
Desc: This is a digitally signed message part
Url : http://lists.freebsd.org/pipermail/freebsd-stable/attachments/20080717/d2c27f62/attachment.pgp