On Wed, Sep 26, 2012 at 12:54 PM, Edward Ned Harvey
(opensolarisisdeadlongliveopensolaris) <
opensolarisisdeadlongliveopensola...@nedharvey.com> wrote:

>  Here's another one.****
> ** **
> Two identical servers are sitting side by side.  They could be connected
> to each other via anything (presently using crossover ethernet cable.)  And
> obviously they both connect to the regular LAN.  You want to serve VM's
> from at least one of them, and even if the VM's aren't fault tolerant, you
> want at least the storage to be live synced.  The first obvious thing to
> do is simply cron a zfs send | zfs receive at a very frequent interval.  But
> there are a lot of downsides to that - besides the fact that you have to
> settle for some granularity, you also have a script on one system that will
> clobber the other system.  So in the event of a failure, you might
> promote the backup into production, and you have to be careful not to let
> it get clobbered when the main server comes up again.****
> ** **
> I like much better, the idea of using a zfs mirror between the two
> systems.  Even if it comes with a performance penalty, as a result of
> bottlenecking the storage onto Ethernet.  But there are several ways to
> possibly do that, and I'm wondering which will be best.****
> ** **
> Option 1:  Each system creates a big zpool of the local storage.  Then,
> create a zvol within the zpool, and export it iscsi to the other system.  Now
> both systems can see a local zvol, and a remote zvol, which it can use to
> create a zpool mirror.  The reasons I don't like this idea are because
> it's a zpool within a zpool, including the double-checksumming and
> everything.  But the double-checksumming isn't such a concern to me - I'm
> mostly afraid some horrible performance or reliability problem might be
> resultant.  Naturally, you would only zpool import the nested zpool on
> one system.  The other system would basically just ignore it.  But in the
> event of a primary failure, you could force import the nested zpool on
> the secondary system.****
> ** **
> Option 2:  At present, both systems are using local mirroring ,3 mirror
> pairs of 6 disks.  I could break these mirrors, and export one side over
> to the other system...  And vice versa.  So neither server will be doing
> local mirroring; they will both be mirroring across iscsi to targets on
> the other host.  Once again, each zpool will only be imported on one
> host, but in the event of a failure, you could force import it on the other
> host.****
> ** **
> Can anybody think of a reason why Option 2 would be stupid, or can you
> think of a better solution?****

I would suggest if you're doing a crossover between systems, you use
infiniband rather than ethernet.  You can eBay a 40Gb IB card for under
$300.  Quite frankly the performance issues should become almost a
non-factor at that point.

zfs-discuss mailing list
  • [zfs-discuss] vm ... Edward Ned Harvey (opensolarisisdeadlongliveopensolaris)
    • Re: [zfs-dis... Freddie Cash
    • Re: [zfs-dis... Tim Cook
    • Re: [zfs-dis... Richard Elling
      • Re: [zfs... Jim Klimov
        • Re: ... Edward Ned Harvey (opensolarisisdeadlongliveopensolaris)
          • ... Jim Klimov
          • ... Edward Ned Harvey (opensolarisisdeadlongliveopensolaris)
            • ... Jim Klimov
              • ... Edward Ned Harvey (opensolarisisdeadlongliveopensolaris)
                • ... Jim Klimov

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