On 11/17/2012 03:03 AM, Richard Elling wrote: > On Nov 15, 2012, at 5:39 AM, Sašo Kiselkov <skiselkov...@gmail.com> wrote: > >> I've been lately looking around the net for high-availability and sync >> replication solutions for ZFS and came up pretty dry - seems like all >> the jazz is going around on Linux with corosync/pacemaker and DRBD. I >> found a couple of tools, such as AVS and OHAC, but these seem rather >> unmaintained, so it got me wondering what others use for ZFS clustering, >> HA and sync replication. Can somebody please point me in the right >> direction? > > Architecturally, replicating in this way is a bad idea. Past efforts to do > block-level replication suffer from one or more of: > 1. coherency != consistency > 2. performance sux without nonvolatile write caches > 3. network bandwidth is not infinite > 4. the speed of light is too slow > 5. replicating big chunks of data exacerbates #3 and #4 > > AVS and friends worked ok for the time they were originally developed, > when disks were 9, 18, or 36 GB. For a JBOD full of 4TB disks, it just isn't > feasible. > > In the market, where you do see successes for block-level replication, the > systems are constrained to avoid #2 and #5 (eg TrueCopy or SRDF). > > For most practical applications today, the biggest hurdle is #1, by far. > Fortunately, there are many solutions there: NoSQL, distributed databases, > (HA-)IMDBs, etc. > > Finally, many use cases for block-level replication are solved in the metro > area choosing the right hardware and using mirrors thus solving #1 and KISS > at the same time.
I understand that replication at the storage level is the Wrong Way(tm) to do it, but I need to cover this scenario for the rare cases where the application layer can't/won't do it themselves. Most specifically, I need to replicate VM backing storage for VMs that can't do software RAID-1 themselves (which is of course the best way). In any case, I'm just looking at what's available in the market now. Ultimate I might go for shared storage + two heads + corosync/pacemaker (I got 'em to compile on Illumos). Cheers, -- Saso _______________________________________________ OpenIndiana-discuss mailing list OpenIndiana-discuss@openindiana.org http://openindiana.org/mailman/listinfo/openindiana-discuss