Remote replication technology

This is probably the wrong site for this sort of question (ServerFault maybe?) and it's also opinion based so - probably - off topic.

But it boils down to them just being different ways of solving a similar problem.

They're both block replication technologies, and it's not like you can mix and match - there's just no way to do SRDF on a NetApp.

Both can do synchronous or async. In both cases - synchronous has all the 'usual' problems of being extremely latency sensitive and requiring you to be doing something sensible at the OS level in the first place. (There's very little point to doing sync replication if your hosts are caching the filesystem, for example - which they almost certainly will be, because performance is awful otherwise)

But pretty much - SDRF is LUN To LUN, where Snapmirror is volume to volume. Both will do sync, async and semi-sync. Both are part of a recovery strategy and are down to managing recovery point and recovery time.

But bear in mind that NetApp is primarily geared around being a NAS - it'll do block protocols, FC and iSCSI, but really it's primary purpose is in network attached storage for NFS/CIFS. Snapmirror works by tracking differences to a snapshot based on an inode table - a filesystem map.

But a Symmetrix is a block storage device, so doesn't have a filesytem layer - replication is block to block. It can't tell about 'filesystem layer' it just does a changed-block replication strategy.

So the 'difference' is "If you buy EMC you get SRDF, and if you buy NetApp you get Snapmirror". (and they may be priced differently). The biggest choice isn't which replication device you use, but rather 'do you buy a NetApp Filer, or a Symmetrix' in the first place.