Spreading RAIDs across multiple DAS enclosures

direct-attached-storageraid

This is really a question of best practice.

In a datacentre environment whereby we have a single MD3200 DAS, and for the sake of the question, 6 expansion cages (MD1200s) how would you configure the RAIDS:

  • One single RAID per cage – i.e. a RAID10 consisting of all the physical disks in one cage, mapped as a single LUN to your servers/clusters. So essentially, we would end up with 7 RAID 10s. This way losing a cage will not affect your other RAIDs/cages.

  • Essentially the same, whereby we end up with 7 RAID10's but the logical disks are actually split across the cages. This way losing a cage may not result in the loss of any data, but could result in the loss of multiple RAIDs.

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Best Answer

You shouldn't daisy-chain the enclosures if you can avoid it

That's also a lot of storage capacity to be planning. Can you give some more detail on what you're doing?

Are you using SAS disks? That's going to be important if you want a resilient cascaded JBOD setup. You'll need the dual-ported disks to make this work well.

See the graphic below. The SAS connections are in a ring topology so that the loss of a chassis can be handled without bring all other JBODs offline.

I suspect the Dell has guidelines on disk group and RAID membership... They are:

Support for RAID levels 0, 1, 10, 5, 6
Up to 120 physical disks per group in RAID 0, 1, 10 
Up to 30 physical disks per group in RAID 5, 6
Up to 512 virtual disks

So this may be a case where you structure your RAID groups to span enclosures. You have a lot of options, though. And complete JBOD or cable failure is uncommon.

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