Ask the Expert

Rolling out a metro-wide SRDF

Would you know all of the hardware and software components needed to roll out a metro-wide SRDF using Symmetrix 5830?

Is it true that you still need multi-hop equipment in order to rollout a good SRDF solution?


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Check out this link to the EMC white paper on multi-hop and the link for more information on SRDF in general.

For those of you who do not know what SRDF is, it stands for "Symmetrix Remote Data Facility." SRDF is an array based remote copy tool that allows data to be copied to a DR site. Using an array-based remote copy solution has its advantages. It does not matter what host platform the data being copied is from. This means you can have many different flavors of Unix and Windows data all being copied at the same time through a single fault tolerant connection to the remote facility.

Software-based solutions would require you to have the software running on all the servers at the productions site AND all the servers at the remote site. That's a lot of licenses. Software solutions can be cheaper at times though. Which one to use depends on how many servers will be affected.

Array-based remote copy solutions are available from many vendors. Compaq, HP, IBM, Sun, Hitachi and others all have remote copy functionality based in the firmware of their storage arrays.

For a metro area remote copy solution, you may not need to use multi-hop, if the distance between the sites is small enough to allow for good production application performance using SYNC remote copy. Multi-hop is normally used to move data over a long distance. The production site will use SYNC copy a "bunker" site. An image is split off at the bunker site and is then copied as a batch process to the final location. The batch copy is called adaptive copy.

The equipment needed for a remote copy solution depends on whether you are connecting to the storage array via Fibre Channel or ESCON. If you are using ESCON then you will need a "channel extender", such as a CNT Ultranet extender, which is used to transfer the ESCON data over IP to the remote location. An extender is required at both sites.

If you are using Fibre Channel, then you can use the newer Fibre to IP bridges like the Inrange 9801 or the CNT Edge.

It will look something like this:

Host--Fibre--8530--Fibre-->CNT<----->IP<----->CNT<--Fibre--8530--Fibre--Host

There are multiple types of array-based remote copy from different hardware vendors:

HP: Continuous Access XP
Compaq: DRM
HDS: Truecopy
EMC: SRDF
IBM: PPRC

Each one has its advantages.

Chris

Editor's note: Do you agree with this expert's response? If you have more to share, post it in one of our .bphAaR2qhqA^0@/searchstorage>discussion forums.


This was first published in August 2002

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