--- On Thu, 4/14/11, Gordan Bobic <gordan@bobich.net> wrote:
> > --- On Thu, 4/14/11, Gordan Bobic<gordan@bobich.net>
>
> DRBD can do active-active, but you'll need a cluster FS to
> achieve that.
Yes I could use a clusterfs (or more precisely a
shared disk cluster fs) with DRBD, but those are
fairly scary currently and do not work reliably
(from what I have read) with DRBD. They were not
designed with drbd in mind.
I could use a distributed clusterfs without DRBD
too, if there were one which were mature,
opensource, and prevented splitbrain properly,
but I have yet to find one (fingers crossed for
ceph someday).
> However
> - what use-case do you have where one guest will fail
> unrecoverably on one machine but resumes working on another
> machine with the exact same FS? In what case would a single
> guest fail without all of them failing?
Think load balancing. Say 10 vservers, split them
so that 5 run on each host normally. If either host
goes down, the other one picks up the slack.
Everything runs slower, but at least it still runs.
> How will it work safely without the inode being marked
> CoW?
Because the whole filesystem is effectively COW, that
is what unionfs and aufs do. They allow you to modify
the fs view without modifying the bottom readonly
layer. The top layer simply stores the deltas. They
are nothing but an FS level (instead of file level)
COW mechanism.
-Martin
Received on Fri Apr 15 00:01:54 2011