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RAID 5 and different disk sizes.

Last response: in Storage
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March 19, 2009 1:05:00 AM

Hello! This is the situation: I have 3 hard drives, 2x 500GB and 1 x 200GB, and I want to set them up in some kind of RAID array (for performance boost).

Ideally, I would have 3x500 GB and I could just set up a nice 1TB hardware RAID 5... But alas, that isn't the case. I'm too scared to do a stripe RAID with both my 500GB, and I want to make use of the storage so I don't want to just mirror them...

So my question is: since it's possible to set up RAID 5 with these drives (with 200GB being the lowest common denominator), i could technically have:

1. 500 GB Drive: 200GB for raid 5, 300 GB unallocated
2. 500 GB Drive: 200GB for raid 5, 300 GB unallocated
3. 200 GB Drive: 200GB for raid 5, ~ 0 GB unallocated

My question is, what happens to the extra 600GB of unallocated space? I know this might sound like a dumb question, but I've never actually implemented a RAID config before. I have a feeling that the 600GB will be usable as two 300GB partitions, but I'm not 100% and would like confirmation or correction. :) 

Also, if anybody can suggest a smart way to configure these 3 drives, so I can maximize performance, I would very much appreciate it!

Thanks!

More about : raid disk sizes

March 19, 2009 1:44:23 AM

just use raid 0
March 19, 2009 1:46:59 AM

Okay, but with RAID 0 I'm a but concerned about the consequence of failure... I'd like some redundancy?
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March 19, 2009 2:16:10 AM


To answer your question, the unallocated space will not be usable. That's just how it is with RAID 5.
March 19, 2009 4:35:29 PM

Ah, that's unfortunate, but good to know all the same...

So I guess RAID 0 is the best choice... I'm a bit reluctant to stripe my drives, as I'm scared of data loss. Does anybody have some experience with desktop RAID and how reliable it is (maybe some MTBF stats?).

Thanks
March 19, 2009 5:21:28 PM

raid 0 ( striping) suffers the same issue
jbod ( spanning) does not

personally i'd raid 0 the 500 gigs and just hook the other drive up for temp/swap space. isolating io across separate drives will often get you better performance than a raid stripe unless your only interested in total throughput.

as for reliablity its really a matter of the drives. ive had drives die after a week and others last 10 years. hard to give mtbf stats if you turn your pc off every night and only use it a couple hours a day then it should last forever. if you pound on the disks 24x7 with uncompressed video or sql then the drives are going to die quicker.
March 19, 2009 5:55:16 PM

Use the 200GB drive for your OS, programs and page file and then RAID 1 (mirror) the two 500GB drives for your data.

You end up with 700GB of useable space with a fair amount of security.
!