SRDF types

Thank Bhat for the answer. Can you please send me that PDF at ajay.kanth@gmail.com.

SRDF/A is also used in environments where the host suffers seriously from running the replication synchronously. I/O respons times can be many times higher compared to SRDF/A. SRDF/A is invisible to thehost, while with SRDF/S the host needs to wait for the ACK from the target array each time.

So it depends: if you need to have ALL data on 2 sites at all times, you'd need SRDF/S, but that comes with a price. If your host suffers too much, consider SRDF/A and perhaps you can tweak the replication cycles to be less than the default 30 seconds.

SRDF/AC Is Adaptive Copy also known as data migration. You should only use this for initial syncing data from source to target since SRDF/DM runs at a lower priority than SRDF/A or /S. But beware: an R2 that's being sync'd with SRDF/DM is NOT to be used as usable copy. Switch to SRDF/A or SRDF/A when all or almost all data is sync'd to the R2. SRDF/DM or SRDF/AC copies data accross the line "out of order" instead of "in order" and since data needs to be written in the right order in order to be usable, you should only use this to migrate large amounts of data in mostly only the initial sync.

Other readers may also be interested in the information provided in this document. Assuming the document is available on Powerlink, if you provide the title, this will enable others to find the document on Powerlink.

I am not sure if this is on Powerlink.. I received this document from one of my friends who had a SRDF session with EMC. SRDF/A -Student Guide.pdf , see if you find it.

Just to add to this good technical discussion as to why you might see someone use SRDF/ACP over SRDF/A.

SRDF/ACP is sometimes used to save on hardware cost (less cache memory requirements) and network bandwidth over SRDF/A. The biggest drawback is really RPO/RTO which will be magnitudes worse at the best you can achieve over SRDF/A. BUT sometimes where bandwidth cost is high or where RPO/RTO requirements are low (24 hour) it is a reasonable alternative.

Having worked in both environments the one nice advantage of SRDF/A over SRDF/ACP is that once it is up and running SRDF/A is much easier to manage as there is less to configure since it is either running or disabled. With SRDF/AR you have to deal with scheduled events which are always more prone to interuption by human error.

Do you mean SRDF/AR or SRDF/ACP or SRDF/DM are one or the same?

Yeah the acronyms do get confusing.

Technically they all relate to SRDF Adaptive Copy where I believe (and could be incorrect) that SRDF/AR and SRDF/DM refer to products from EMC used to control SRDF/ACP (a mode refering to SRDF in Adaptive Copy) replications.

See Adaptive Copy is already more confusing than SRDF/A and that is just based on the supporing products

SRDF / AR = Symmetrix Remote Data Facility / Automatic Replication, used between at least 3 DMX's
SRDF / S = SRDF / Synchronous
SRDF / A = SRDF / Asynchronous

SRDF / DM = SRDF / Data Mobility is in fact the acp_disk mode you can use for /S and /A to "catch up". An empty R2 will usually need the acp_disk mode to get the data from the R1.

Usually EMC Global Education calls "Student Guide" documents used while delivering customer trainings.. Usually it's copyrighted material, not ment to be shared between customers.

Search for SRDF cli guide in powerlink, you will find it. Its complete SRDF guide which discuss about the adaptive copy also.

regards,
Saurabh