On Wed, 2008-09-10 at 19:10 -0400, Maurice Volaski wrote: > >On Wed, 2008-09-10 at 18:37 -0400, Maurice Volaski wrote: > >> >On Wed, 2008-09-10 at 15:00 -0400, Maurice Volaski wrote: > >> >> >On Wed, 2008-09-10 at 14:36 -0400, Maurice Volaski wrote: > >> >> >> A disadvantage, however, is that Sun StorageTek Availability Suite > >> >> >> (AVS), the DRBD equivalent in OpenSolaris, is much less > >>flexible than > >> >> >> DRBD. For example, AVS is intended to replicate in one direction, > >> >> >> from a primary to a secondary, whereas DRBD can switch on the fly. > >> >> >> See > >> >> >> > >> http://www.opensolaris.org/jive/thread.jspa?threadID=68881&tstart=30 > >> >> >> for details on this. > >> >> > > >> >> >I would be curious to see production environments "switching" > >> direction > >> >> >on the fly at that low level... Usually some top-level brain does > >> that > >> >> >in context of HA fail-over and so on. > >> >> > >> >> By switching on the fly, I mean if the primary services are taken > >> >> down and then brought up on the secondary, the direction of > >> >> synchronization gets reversed. That's not possible with AVS because... > >> >> > >> >> >well, AVS actually does reverse synchronization and does it very > >> good. > >> >> > >> >> It's a one-time operation that "re-reverses" once it completes. > >> > > >> >When primary is repaired you want to have it on-line and retain the > >> >changes made on the secondary. > >> > >> Not necessarily. Even when the primary is ready to go back into > >> service, I may not want to revert to it for one reason or another. > >> That means I am without a live mirror because AVS' realtime mirroring > >> is only one direction, primary to secondary. > > > >This why I tried to state that this is not realistic environment for > >non-shared storage HA deployments. > > What's not realistic? DRBD's highly flexible ability to switch roles > on the fly is a huge advantage over AVS. But this is not to say AVS > is not realistic. It's just a limitation. > > >DRBD trying to emulate shared-storage > >behavior at a wrong level where in fact usage of FC/iSCSI-connected > >storage needs to be considered. > > This makes no sense to me. We're talking about mirroring the storage > of two physical and independent systems. How did the concept of > "shared storage" get in here?
This is really outside of ZFS discussion now... But your point taken. If you want mirror-like behavior of your 2-node cluster, you'll get some benefits of DRBD but my point is that such solution trying to solve two problems at the same time: replication and availability, which is in my opinion plain wrong. _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
