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unusable disk space
we have around 4TB free space on disks from disk group. But, device (17gb raid 5 3+1) creation failed with error
"The requested device(s) cannot be created because the mirrors cannot be distributed according to protection requirements¿
I would like to know that anyway the disk space can be utilized ? thanks
"The requested device(s) cannot be created because the mirrors cannot be distributed according to protection requirements¿
I would like to know that anyway the disk space can be utilized ? thanks
MarcT2
131 Posts
1
July 16th, 2008 04:00
It's desirable for a disk containing multiple RAID5 hypers to have all the other RAID members (the raid "rank") on the same set of physical drives. eg for a drive containing 10 RAID5 7+1 volumes, all other RAID members should be on the same 7 physicals so that only 8 drives are involved in total. This is the "raid group". If one drive fails, the probability of a second drive in the remaining 7 failing is very low, so the probability of data loss is small.
Shotgun RAID occurs when the RAID ranks don't all belong to the same physicals.
In the worse case scenario, if the 10 RAID5 7+1 volumes had their other RAID members on completely different physicals then there are now 80 drives involved in in the raid group. The probability of data loss occuring in the event of a double drive failure is significantly increased, because if the first drive fails some data loss will occur if any of the remaining 79 drives also fails.
Symconfigure, ECC & SMC all use SymmWin (which runs on the DMX service processor) to distribute new volumes when you create them. SymmWin has RAID5 affinity rules to distribute RAID5 volumes over different hardware paths (directors & loops), power zones and port bypass cards. It also tries to avoid shotgun raid.
It would appear you have fallen foul of the affinity rules. The best course of action is to get an EMC CE or Configuration RTS involved to have a look at the binfile and see what can be done. Balancing up the number of splits on a group of drives can help in some situations for example.
Let us know how you get on!
Marc
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July 16th, 2008 05:00