[Linux-cluster] GFS2 support EMC storage SRDF??

[Bryn M. Reeves]

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.

Regards,
Bryn.