I am concerned with EMC SRDF applications. Mainly, what is the theoretical maximum latency that SRDF synchronous disk mirroring can handle before timeout problems occur? As well, when mirroring between Symmetrix systems, is there a number of underlying threads that carry individual volume IOs? If so, is there an average number of threads or a maximum number of threads? This information would be greatly appreciated. However, in my searching to date I have found none who can help me with this. There also seems to be no literature on SRDF that is this detailed. Any help?
Thanks a lot.
Latency timeouts depend on whether you are using ESCON or Fibre links for remote copy. The link type also affects latency. DWDM over dark Fibre will have less latency then a leased T3 link. I would need to know your link types, bandwidth, which extender vendor device you are using (CNT, ADVA, Inrange, etc.).
All these aspects affect how far you can go. Most extenders provide buffering and/or compression to reduce latency concerns on the storage side. The type of application you are using is important also. I imagine since you are concerned about latency that you are using SYNC SRDF. Using SEMI-SYNC may help a bit since you can be one write behind. If that is an issue for you, and you are going long distance, then Adaptive copy may be your only choice. Adaptive splits off a BCV and copies it at a later time.
I have not been able to find many details on SRDF either. Perhaps an EMC engineer can help you get to the level of detail you want.
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This was first published in May 2002