[Linux-cluster] GFS2 support EMC storage SRDF??
Bryn M. Reeves
bmr at redhat.com
Tue Dec 13 14:43:10 UTC 2011
On 12/12/2011 03:29 AM, yu song wrote:
> My question is that GFS2 supports SRDF ?? looking at KB in redhat site, it
> only says that GFS2 does not support using asynchronous or active/passive
> array based replication. but it seems like does not apply for SRDF.
SRDF offers both synchronous and asynchronous replication but is
active/passive. I.e. the administrator can configure whether the primary
(R1) site waits for write acknowledgement from the remote (R2) site or
not but at any one time it is only possible to write to either the R1 or
the R2 device.
Synchronous replication guarantees write order fidelity for the R2 copy
and ensures the remote copy is crash consistent at all times.
Asynchronous replication allows SRDF to support longer distances (or
lower bandwidth / higher latency inter site links) by packaging multiple
writes into delta sets to be sent to the remote site.
More complex modes and combinations exist that allow consistency to be
maintained among a group of devices, for example a database's data store
and redo logs, or that relax some of the synchronous replication
guarantees to improve efficiency (semi-synchronous operation).
Active/passive in the context of storage replication usually refers to
the states of the devices on the two sites. In active/active replication
both sides are fully active at all times and writes may be issued on
either side of the replication (a bit like multi-master application
layer replication). An active/passive design only allows one side to be
active for writes at a time.
Most array based implementations are active/passive and offer
asynchronous, synchronous or semi-synchronous operation.
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