Host Based versus Array Based Symmetrix Replication

Let me start by asking if you stop the host based replication, the response time gets better? This way we can relate is it really the replication that is impacting the performance or its something else? If its something else then be it host based or array based wont make much difference.

In my opinion most ppl have started adopting the application based replication because of the consistency and ease in bringing the app online after a disaster.

Some more information regarding the application, type of replication can help understanding the problem better.

regards,

Saurabh Rohilla

EMC has 2 host based migration softwares. PPME and Open Migrator.

PPME uses different techtypes. There are two kind of data migration a. Bulk Data that is already on the device and b. Fresh write I/O coming on the device from Application writes. PPME offers you a mix of technologies.

1. HostCopy - Here in the bulk datacopy uses the Host Resources. Hence Need to check if the Host is highly utilized, then using HostCopy can add further impact on Host since it will also need some resources on the Host. I/O Cloning is done by Powerpath Data Migration driver.

2. TimeFinder Clone- This can be used where the data is to be migrated from one device to another on the same VMAX. It uses the advantages of the TimeFinder Clone to move the Bulk Data. Fresh Write I/O still are cloned using PPME driver. (It remains same in all the techtypes)

3. Open Replicator - This can be used where the data to be migrated from one device on one storage array to target device on another storage array(it may be clariion or VNX or supported models of HP EVA or Hitachi). It uses the array based migration feature of OR and Fresh Write I/O are still cloned using PPME.

4. Invista.

All these Powerpath Migration Enabler technologies help in Online data migration from the source to the target. No or minimal application downtime is there. Only downtime is in case of Windows Server 2008 Clusters where in you are migrating the cluster resources, that the Cluster group has to be brougth offline when you commit the changes and then you can bring it back online. In case the servers are not in cluster, no downtime is required.

Open Migrator is another Utility. It can do the volume based migrations. It can migrate the data from a device with any raid type, on any external storage to any other raid type on any other external storage. requirement is both the source and the target devices should be presented to the same host and should be visible in the Disk Management.

Host based migration solutions do not have any license costs involved. Open Migrator is free software. Powerpath Migration Enabler needs a Technology type license, but it will be free if you already have Powerpath license for the site. However it will require the respective licenses for different technologies like Timefinder/Clone and Open Replicator. HostCopy has no costs associated with it.

Array Based Replication features i would say are much faster. SRDF/S is the best for data migration on luns if the distance between two VMAX is very less and running a command for failover can bring the device online on the Remote site. It also does not add any performance costs on the applications. Open Replicator is another software, here depending on the technology you are using, Downtime may be required.

Array based replication features will require licensing requirements to be taken care of.

• Please mark this reply 'answered', if this answers your query.

why are we talking about migration if OP is concerned with replication.

Thanks for all the replies guys..interesting that host based replication is becoming more popular.

Looks like the performance in this case is on the backend.

Answered