Low-bandwidth LUN mirroring

eal · Mon Oct 13, 2008 9:24 am

This is the scenario:
- two plants A and B with Windows network
- people at plant A produces and uses documents
- people at plant B uses documents produced by people at plant A
- plant A and B would like to live share documents
- plant A and plant B are connected with a 4 Mbit/s link (almost full)

People at plant B do not need to write in the shared area.

Is StarWind, with its low-bandwith replication feature, suited for such a task?

Is it possible to use the mirrored LUN in r/w mode in plant A and in read-only mode in plant B?

Mon Oct 13, 2008 9:26 pm

It's not gonna work unfortunately... Please read this:

http://www.starwindsoftware.com/forums/ ... php?t=1392

eal · Wed Oct 15, 2008 12:17 pm

Do metadata and data stored in a mirrored LUN get corrupted if an initiator connects in read only mode to copy 1 of the LUN and another one connects in r/w mode to copy 2 of the LUN?

Or does setting replication active between two copies of a LUN require r/w to be enabled on both copies?

Just asking. Thank you in advance.

Wed Oct 15, 2008 3:29 pm

Yes of course. B/c even reader has no clue about writer changing disk content on the other initiator. So either many readers OR only one writer. No mixes. Or distributed lock manager (MetaSAN) or cluster-capable file system (SANbolic MelioFS or DataPlow SFS).

Second replicated node is not mounted. It's backup node you'll manually mount of first one will go down. No zero downtime in this case.

eal wrote:Do metadata and data stored in a mirrored LUN get corrupted if an initiator connects in read only mode to copy 1 of the LUN and another one connects in r/w mode to copy 2 of the LUN?

Or does setting replication active between two copies of a LUN require r/w to be enabled on both copies?

Just asking. Thank you in advance.

eal · Fri Oct 17, 2008 12:57 pm

Thanks, Anton, for the hints. It seems my scenario fits in metaSAN.

I've seen there is a guide in your library to use metaSAN with StarPort.

My only unanswered question now is if low-bandwidth LUN mirroning can be band constrained and if replication may be set synchronous or asynchronous.

Sat Oct 18, 2008 11:55 am

We do pseudo-async replication but it really depends on load and link performance will it be OK or not. So you can try before you buy

eal wrote:Thanks, Anton, for the hints. It seems my scenario fits in metaSAN.

I've seen there is a guide in your library to use metaSAN with StarPort.

My only unanswered question now is if low-bandwidth LUN mirroning can be band constrained and if replication may be set synchronous or asynchronous.