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I know that the slower disk will constrain speed and the smaller disk will constrain size.

Is it possible to use the extra space on the larger disk in some fashion (ie. as a separate, non-striped partition)?

In my case, this would be with the onboard raid of the motherboard. It is provided by the southbridge, the Intel ICH10R. I'd be interested in Windows XP and Linux situations.

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Hardware or Software RAID? What OS? –  MikeyB Jul 9 '09 at 2:14

6 Answers 6

up vote 6 down vote accepted

Can and should are two very different things. Even with software raid where you can use the unused portions of the drives for other tasks I would argue that it's a bad idea.

Performance is the only reason to run RAID0. In a RAID0 the IO operations are stripped across all the drives. Now you want a few of those drives to be doing other things on the side. This additional I/O will slow down these disk and as a result will degrade the performance of the entire RAID0 array.

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Spot on. Kind of like using a sports car to tow a trailer. –  John Gardeniers Jul 9 '09 at 3:37
    
Thanks. So it is possible (under some set ups). I totally understood that using it on the side would destroy the speed advantages of a raid 0 set up. –  Albert Jul 9 '09 at 4:04
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With software raid it's certainly possible. You just need to partition the larger disks with a partition that is the same size as the smaller disks. Then you can use the remaining disk space as you see fit. Again I wouldn't recommend it but it is possible. –  3dinfluence Jul 9 '09 at 4:19

In theory there's no reason why you can't do this, and it'd be easy enough with software raid in linux. Whether you can do it or not will depend on your raid controller, but it should be possible.

Linux support for fakeraid (which i would guess you have) is fairly terrible though, I wouldn't expect it to work at all on linux.

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A person on some forum posted that you cannot use the extra left over space.

http://icrontic.com/forum/showthread.php?t=47115#post406258

I've reposted his answer here incase icrontic disappears before serverfault does:

Could I partition a second larger drive with one partition the same size as the first smaller drive and a second partion with whatever space is left, and then RAID 0 the first drive and the matching partition of the second drive. Then, could I have a left over partition as an extra storage volume?

No you couldn't. When a RAID controller downsizes a drive all remaining space is gone and not accessable as long as the drive is part of an array. It does this because the drives are not spanned as everyone thinks. They are striped together. In otherwords woven together. If you write a 32Kb file to a 2 drive RAID-0 with an 8K stripe it writes 8K to drive 1, 8K to drive 2, 8K to drive 1, and 8K to drive 2. So 32K is written in 4 alternating chunks to 2 drives. Therfore both drives must exactly match on space.

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Well, if it was on a forum it must be true. This may be a limitation of someone's specific raid controller, but there is in general no such limitation. –  theotherreceive Jul 9 '09 at 7:04

If speed is not the primary goal of your RAID-0 setup (although it likely is, but in that case, why not buy matched disks?) then you can simply add both disks to the same volume pool and use them as a concatenation instead of striping across.

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If you can stand linux software raid, than why not ? As long linux md uses partititions as primary devices, you can create same size partitions on your different drives and use leftover space too. Of course, i wont recommend that for serious task, but it might work for you.

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The technology/term you are looking for is called short-stroking and has been described in this question.

Unfortunately even if it were a safe or sensible thing to do in a RAID0 setup, it's highly unlikely that your onboard controller would be capable of doing so.

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