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How does Synchronous SRDF handle multi-pathing?

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Greetings Everyone,

I am wondering how SRDF handles multipathing.  For example, we have a source and target array in different data centers.  Each array has two RA-ports.   These RA-ports are connected via two separate, geographically diverse InterSwitch Links (ISLs).

What happens during an SRDF transmission if I lose one of these paths?  Does the VMAX/RAport know to retransmit?

Any input is appreciated.  Whitepapers and documents are appreciated even more.

Regards,

Julianne

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Re: How does Synchronous SRDF handle multi-pathing?

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I would recommend checking the SRDF Connectivity guide as well, however, some customers may find it a bit advanced so to make the long story short and without going into further FC details,

VMAX uses Parallel IO/ RoundRobin mechanism for load balancing for RF dirs. Around 2000-2500 IOPs are sent out of each RF director slice( CPU can take more than that but this is the average number i have seen through many boxes), You cannot limits the IOPs per each RDF director slice so a fairness mechanism will try to ensure that IOPs are evenly balanced across RF dirs. This applies to SRDF/s for SRDF/A it is a bit different as available caching is taking into considerations.

For REs, It works by establishing tcp sessions from one RE to all REs in the remote arrays

@Aran has detailed this in another Community thread.

https://community.emc.com/message/825217?et=watches.email.thread#825217

Hope this helps

Mohammed Salem

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Re: How does Synchronous SRDF handle multi-pathing?

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symm retransmits a packet if ACK is not received by the source...i have not checked the doc myself but srdf connectivity guide should have some info on this..

regards,

Saurabh rohilla

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Re: How does Synchronous SRDF handle multi-pathing?

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I don't think the SRDF product guide goes into that much detail.

As Saurabh says, The SRDF links are fully redundant. If one fails, it is transparent to host operations. IO's will be re-driven down the remaining available paths. When the link is back on-line, traffic will be directed to it without user intervention.

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Re: How does Synchronous SRDF handle multi-pathing?

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not the product guide, srdf connectivity guide should have this info...

regards,

Saurabh Rohilla

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Re: How does Synchronous SRDF handle multi-pathing?

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EMC recommends that the Symmetrix system has at least two director board sets for SRDF protection; one processor on each board for SRDF to provide redundant links in case a communications link fails.

SRDF connectivity guide

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Re: How does Synchronous SRDF handle multi-pathing?

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I would recommend checking the SRDF Connectivity guide as well, however, some customers may find it a bit advanced so to make the long story short and without going into further FC details,

VMAX uses Parallel IO/ RoundRobin mechanism for load balancing for RF dirs. Around 2000-2500 IOPs are sent out of each RF director slice( CPU can take more than that but this is the average number i have seen through many boxes), You cannot limits the IOPs per each RDF director slice so a fairness mechanism will try to ensure that IOPs are evenly balanced across RF dirs. This applies to SRDF/s for SRDF/A it is a bit different as available caching is taking into considerations.

For REs, It works by establishing tcp sessions from one RE to all REs in the remote arrays

@Aran has detailed this in another Community thread.

https://community.emc.com/message/825217?et=watches.email.thread#825217

Hope this helps

Mohammed Salem

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