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March 26th, 2014 05:00
Storage Pools: How to determine RAID Groups and associated LUNs
Hello everybody
I am quite new to all the EMC Storage stuff but i am very interested and I already learned a lot of things! It is a pleasure for me to be part of EMC and the community.
Well i have the following question for you guys:
If i create a storage pool with let's say all the available disks of the storage and i choose a RAID5 for the RAID Layout. How can i determine where the individual RAIND Groups are located and where are the LUNs which are associated to the RAID Groups?
If i create individual RAID Groups it is not a problem for me to determine the LUNs on it, but i don't see a way to see the same if i work with Storage Pools.
Do you guys know how to see this stuff?
Thank you so much for your help and sorry for lack of knowledge or bad english =)
Best regards
dynamox
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March 26th, 2014 06:00
pools are comprised of private raid groups, pool LUNs are spread over private raid groups in 1G slices.
DukeR1337
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March 26th, 2014 06:00
Okey that means every single LUN is spread over all disks resp. RAID Groups?
Best regards
umichklewis
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March 26th, 2014 07:00
More accurately, it means that each LUN takes 1GB slices of every private RAID group created in the pool. One way to think about it, is that every physical spindle in the pool can service I/Os for the LUNs within that pool. The physical location of where a LUN sits on which drives within the pool doesn't usually matter, unless you have specific performance requirements or need very consistent performance for each LUN. In those cases, RAID groups are preferable to Pools, since RAID groups have less overhead than Pools.
DukeR1337
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March 26th, 2014 08:00
Hey
Thanks a lot for that detailed answer. That means also that there is also a higher protection of every single LUN due spreading out over more than one raid group, isn't it?
AdamFox
254 Posts
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March 26th, 2014 08:00
Exactly. If I had 8 RAID-5 RAID groups, one the one hand I could survive as many as 8 simultaneous drive failures, on the other hand, I could die on my 2nd failure. It just depends on which drives fail.
dynamox
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March 26th, 2014 08:00
failure domain
- two failed drives in a raid-5 private group will potentially take out entire pool.
AdamFox
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March 26th, 2014 08:00
Potentially, yes. I would say it's definitely not worse and could be better. I can lose more drives in a pool as long as those drives are spread across the private RAID groups such that none ever go past the protection of the RAID group. However, a classic RAID group and a private RAID group of the same type and width are protected exactly the same and it only takes one RG failure to take out the LUNs associated with it. But that was the same with classic LUNs and Metas. That's why I say it's at least equal and potentially better.