On 15/05/2006, at 3:38 AM, Eric Fluger wrote:
-- -- syncronous (real time) mirroring is best if it is practical,
however, asyncronous ackowledgements can be acceptable if both the
primary and secondary mirrors do not have be accessble to users at
the same time, which is the case if i understand the problem
description correctly.
-- -- i definately suggest taking a look at sun availability suite,
specifically the "geographic cluster edition." sun-cluster has
provisions for syncronous mirroring and the geographic edition,
which is designed for use over large geographic areas, has
provisions for asyncronous mirroring.
-- -- the main attraction of rsync style solutions is their ability
to work with high latency communications between sites. from
cursory examination, it appears thet the asyncronous mirroring
features in sun-cluster geographic edition solve the same problem,
and in a better way than rsync. setup may be more complex for you
though.
-- it's been some time since i worked with sun-cluster, and i
haven't used the geographic edition. it would be nice to get some
input from someone who has.
Without commenting on the rest of the email, about general
availability solutions, I *can* say something about Geo Cluster.
Basically, SunCluster, Geographic Edition allows you to make a
"cluster of clusters", where node-to-node failover at either end is
used to allow synchronous mirroring and host failover, and the two
clusters allow (manually initiated) failover for DR purposes. Either
or both clusters can be a one-node cluster.
Data mirroring is performed by a local volume manager within a
cluster, and by the portion of availability suite called "Remote
Mirror" (formerly known as SNDR). This component can be used
independent of SunCluster, in which case application failover is your
own problem.
Remote Mirror inserts itself just above the block device level and
allows both synchronous and asynchronous mirroring. Async uses a
bitmap to record changed regions. This allows interruptions to the
data path to be dealt with, including halting mirroring as needed.
What it does *not* provide is any administrative interface to reverse
the mirroring, short of tearing down the mirror and re-creating in
the opposite direction. Geo Cluster adds a layer of admin tools that
automate this process.
HTH
Boyd
Melbourne, Australia
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