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1TB versus 2TB RAID 6 and RAID 10

Posted on 2013-06-14
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Last Modified: 2016-11-23
I'm considering using 2TB drives in a RAID 6 or a RAID 10 configuration.  I'm concerned about the rebuild time...   Recently using a Dell Perc 5/i controller I saw a 1TB member in a RAID 10 array take 4-5 days to rebuild.  Does this mean it could take almost two weeks for a 2TB RAID 10 member to rebuild?  Also, does RAID 6 take even longer to rebuild?
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Question by:gopher_49
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Expert Comment

by:dlethe
ID: 39248186
Not necessarily. It took 4-5 days because the surviving disks had a bunch of recoverable read errors, so it could have taken 4-5 seconds, assuming enterprise drives to get a 512 byte chunk., and I expect system was booted and doing a lot of I/O on it's own so rebuild was low priority.

In perfect world where you have enterprise drives and no such problems with deep recovery, and the system isn't booted so not competing with other I/O ... rebuild should run at near media speeds in a RAID10.  If the HDD is capable of writing at 100MB/sec sustained, and you have 1000MB disk drives (to make the math easy), then it should have taken 2 x 1000/100 seconds.

Now in a RAID6 rule-of-thumb for a rebuild using 5 disks, each 1000MB, and that same 100MB/sec transfer on that controller, maybe (5 - 1) * 1000/100 seconds    (roughly)
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Author Comment

by:gopher_49
ID: 39248390
So,

It is safe to use 2TB SATA drives in a RAID 6 or 10 config?  I assume I need to purchase the better quality drives...
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dlethe earned 250 total points
ID: 39248484
Yes, you need enterprise class SATA drives, and not just any enterprise class, such as the WD drives.  Dell doesn't certify them.  Go with the Seagate ES family of enterprise SATA.  Look at the constellation class on their website.  Or if you prefer to get Dell support & warranty, contact them and they'll be happy to sell you the right drives.
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Assisted Solution

by:Andrew Hancock (VMware vExpert / EE MVE^2)
Andrew Hancock (VMware vExpert / EE MVE^2) earned 250 total points
ID: 39248546
Really depends on your disks, do you not have any other servers you can move VMs to, so no I/O is occuring on the server, whilst the rebuild is taking place.
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Author Comment

by:gopher_49
ID: 39248688
I'll have vMotion in this new environment... And I typically get Seagate ES Constellation drives....  Sounds like I'm good.

thanks!
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