Link Speed for CA Replication With EVA 4400 And Question

[Osama Odeh_1]

if the link speed between two site(WAN connection) not enough for CA Asynch or synch ; does this impact the source storage specially EVA 4400. and produce IO performance issue make a busy connection.

thnx in ADV.
o.odeh

[IvanForceville]

The impact is pretty huge.

In a CA sync replication the source EVA waits for the acknowledge of the target EVA before continuing which leads to performance degradation of the production.

In an asynch replication you need to size a WriteHistoryLog which is a buffer for unsend IO's. You can size this up to 2TB but this data is unprotected when the EVA fails.
Also, when the WriteHistoryLog is completely full CA switches from Async to Sync replication to push all the data in the WriteHistoryLog over the link...

And that my friend is not a situation where you want to be in.

You can however set the WriteHistoryLog to a certainsize ex. 1GB and gradually extend this when needed. But, be aware that you can't decrease the size.

[Uwe Zessin]

> You can size this up to 2TB

Watch out, as this is an internal virtual disk in VRAID-1, so it will take 4 TeraBytes...

[Osama Odeh_1]

the bandwidth speed between two site 5mbs and this speed not didicated for HP CA replication we have 3-4 mbs availble from this bandwidth , so when we create any DR group wth any vdisk

we found the following message many time in event log:

"Excessive PING response time on the inter site link is preventing acceptable replication throughput: Reducing data exchange resources"

[Adeniyi Adeyemo]

Because the link is not dedicated to CA, you will see "Excessive ping Response...." messages whenever there is heavy traffic on the link. I have seen this happening on my replication link majorly during the night when there is backup transaction over the link.
If you are using MPX,depends on the firmware on the MPX,no of PING supported by the mpx were increased in the most recent firmware update.

[Osama Odeh_1]

still I need answer for simple qustion

if we have low bandwidth between two site for ca replication also with Asynch
how this will be affected the source EVA 4400 and LUNs pathsc losted due to this performance issue.