Raid 50 on odd number of disks?

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Kyv

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I have a question about raid 50. Can it run on a odd number of drives? I have a new server for security cameras and it has 16x 1tb NL SAS drives which will be used for video archiving (64 live cameras) and will have heavy write IO.


I was thinking of setting it up as a raid 50 with 15 drives and 1 drive as a hot spare. Is this possible or would it have to be 14 drives for a raid 50? I did think of doing raid 6 with with 15 drives but then thought it would not be a good idea because of the higher write penalty.

Any feedback would be appreciated.

Thanks!
 
You can run RAID 50 with your 15 drive set with out a problem. As Dan said, RAID 50 is just a nested levels of Raid, multiple RAID 5 sets all striped together in RAID 0. In your case, it would be 3 RAID5 sets of 5 drives all striped together in RAID 0, with you 16th drive as a global spare for any of the RAID5 sets. RAID 50 can take on multiple forms depending on the total amount of drives. For example, with 12 drives, you could do a 2X6, 3x4 or 4x3 scenarios.

What controller are you planning on using?
 
The controller will be a PERC H710P on a PowerEdge R720xd server.

There would be 12 TB of usable space in such a instance of a 15 Drive raid 50 due to the 3 disks being lost for parity correct?
 
That's correct, 12TB RAW, assuming 1TB drives. Figure 11TBish usable after overhead.
 
Another thing to keep in mind is to ensure you have good, up to date backups. Your 15 drive RAID50 is just a slightly less scary RAID5 in the failure sense. Up to 3 drives in this scenario can fail, if they are the right 3 drives (one drive in each of the 3 R5's, which will leave your striped parity set up). Unfortunately, if the wrong 2 drives fail (2 drives in the same parity set), your array goes tits up. A hot spare rebuilding your array can help if it lives to complete the rebuild and no other members fail, but with larger array members the time required and the prevalence of Murphy's law RAID 6 is a MUCH better choice in >8 drive arrays.
 
I would have used RAID6 on 15 drives and 1 hot spare, not RAID50 in one or the other combination. Better space utilisation and added reliability.

With so many concurrent writes (64 writers) I would personally have opted for RAID10 instead of the parity based RAIDs, but that may not be an option for you (how much space do you need?)
 
I've never heard of RAID 50 with more that two RAID 5 sets. Is it possible not all RAID controllers support this?
 
marsboer said:
I would have used RAID6 on 15 drives and 1 hot spare, not RAID50 in one or the other combination. Better space utilisation and added relia. lity.

With so many concurrent writes (64 writers) I would personally have opted for RAID10 instead of the parity based RAIDs, but that may not be an option for you (how much space do you need?)
Click to expand...

Raid 10 wasn't an option because of price. Server as it was cost little over 12 grand so to do raid 10 with the space that is required would of cost about 20 grand. Server needs a minimum of 10+ tb for 30 days of motion detected video retention.
 
Ahhh, Camera storage. You mentioned an H710P, and it's fairly speedy compared to most, so go with RAID6 and call it done. You'll lose 2 drives worth of capacity rather than 3 for the RAID 50 setup. A Hot spare is still a good idea though.
 
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