ORIGINALLY POSTED 1st March 2013
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One of the internal, and IBM Business Partner mailing groups I subscribe and participate in ( Hi to all on Diskcore ) recently debated :
Want to know whether IBM V3700 are true symmetric active active controllers.
A response was made, but also asked :
Can you define what you or the customer means exactly by true symmetric active/active disk controller?
The whole “preferred” status of a vdisk is an attempt to load balance.
So when you create volumes…
vdisk id = 0 - preferred to node 2 vdisk id = 1 - preferred to node 1 vdisk id = 2 - preferred to node 2 etc
The idea being, if a multipath driver understands ALUA (preferred) then overall you spread your load over both nodes. (control canisters) So load balances at a lun level. If a multipath driver does not understand or use ALUA then it will round robin I/O across nodes. So load balances I/O within a lun.
In both cases, all SVC derivatives will behave the same.
- reads will be processed by which ever node received the read request.
- writes will be acked by the node that received the write request after it is mirrored to the partner node
- the “owner” node – i.e. the preferred node will be the one that owns doing the actual destage from cache to disk
- so the default “ALUA” assignment still applies for writes, i.e. it load balances write to disk operations at a lun level.
All said and done…
It makes no difference, and, SVC, V7000, V3700, V3500, Flex System V7000… they are all ACTIVE/ACTIVE and don’t let any EMC propaganda tell you otherwise