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building a RAID6 array with different disk sizes

Posted on 2014-04-24
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I am building a virtual environment on a R710 server with PERC/6i controller. I am planning to go with a RAID6 array. I have four(4) 500 GB hard disks and two(2) 750 GB hard disks. Can I combine these and create 1 RAID6 array? The controller is showing me that I can get about 2.7 TB with this combination. Is it possible to build one array with different hard disk sizes and get the entire space or am I losing 250 GB on each of the 750 DB hard drives. Also the two(2) 750 GB disks on my Dell Poweredge R710 are displaying amber light after an initial green light (comes with green then changes to amber on and off). Is this because of this discrepancy? The drives are new and in good condition. The controller is not showing any errors on these two disks.

Thanks,
Bhaskar
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Question by:bnss
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rindi earned 1500 total points
ID: 40022127
You will waste the extra space on the larger disks. If I were you, I'd get another 2 500GB disks and use the 750GB ones for something else.
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by:Seth Simmons
ID: 40024036
I am building a virtual environment...planning to go with a RAID6 array.

i personally would have gone with raid 10.  i had an older dell server with raid 5 and after changing to raid 10 did noticed an improvement with vmware guests.  raid 5/6 is good for a lot of reads but is a bit slower with writes due to parity; 10 is better when you have equal amount of reads and writes

Can I combine these and create 1 RAID6 array?

technically feasible but not ideal

The controller is showing me that I can get about 2.7 TB with this combination.

sounds right.  with 6 disks at 500gb it will be a little under 3tb raw.  as a raid 5 your usable space would be about 2.4tb and as a raid 6, probably about 1.8tb; 1.4tb in raid 10

...or am I losing 250 GB on each of the 750 DB hard drives

correct. when you have different size drives selected for an array the total used space of each disk will be the size of the smallest disk.  in this case it's 500gb which means on the 750gb drives only 500gb will be used.  

...are displaying amber light after an initial green light...

amber lights appear when something is wrong with the hardware; wouldn't do that from a raid configuration.  flashing amber light indicates a failure; alternating between amber and green means predictive failure.  if the controller shows nothing wrong i would recede the drives and see if it still occurs.
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Author Comment

by:bnss
ID: 40024493
i personally would have gone with raid 10.  i had an older dell server with raid 5 and after changing to raid 10 did noticed an improvement with vmware guests.  raid 5/6 is good for a lot of reads but is a bit slower with writes due to parity; 10 is better when you have equal amount of reads and writes

This is a dev/test environment and disk space is more important so we can host multiple images. In such a scenario, would you recommend RAID10?

Thanks,
Bhaskar
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Expert Comment

by:Gerald Connolly
ID: 40024618
If its dev/test and you don't need to dev/test RAID-6 (or RAID10), RAID-5 will be perfectly adequate.
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Expert Comment

by:rindi
ID: 40024701
Actually for testing purposes I'd probably use RAID 0 as there is no need for disk redundancy then., and with RAID 0 you get most speed and you can use the total size of the disks.
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