Drobo did it somehow - i.e. they can mix and match multiple sizes of discs, as long as 2 biggest discs have the same size. Is there any solution for this type of storage, free, for Linux?
6 Answers
The LVM HOWTO should be helpful.
Yes. Linux standard software raid can handle that.
For me, it's 2 hard disks, 250 and 200 GB. Each disk has raid partition of the same size, and mirrored using software raid. Works lovely.
I didn't heard of any hardware raid which is able to work with non-equal hard disks.
answered Sep 18, 2009 at 10:48
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From what you describe - it's can't handle it. I.e. you use only 200GB of the smaller drive.– user13185Sep 18, 2009 at 11:06
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3The extra space isn't wasted though. It just isn't part of that particular RAID array. There is nothing to stop it being used for something else. If you have three drives, say 250+250+200, you could have a 200Gb RAID5 and the remaining two lots of 50Gb as a RAID1 array. Use LVM to join them if you want a single filesystem. It should handle failure of a drive containing parts of both arrays cleanly. There is no easier way that I know of though. You could try using the FUSE port of ZFS I suppose. Sep 18, 2009 at 11:25
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And I want a system that can effectively use full capacity of drives of various sizes - just like Drobo.– user13185Sep 20, 2009 at 10:03
This article may help you to understand how LVM works.
Hardware RAID systems that I've used will let you use different size hard drives, but any extra space is wasted. I've heard that some of them let you use extra space as a non-RAID partition too, but I've never personally seen one like that.
answered Sep 18, 2009 at 11:39
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Check what Drobo does.– user13185Sep 20, 2009 at 10:02
There is a way, I read an article on it a while back - http://www.linuxjournal.com/article/8149 It's not exactly what you're asking for, it is about using ATA over Ethernet and uses EVMS (dead project for a while now), but it's close.
Thing is that if you really need this functionality, you either need to pay with $$ for a DROBO and be able to have it Just Work (I have one and have had no issues with it) or pay with your time to hack around and deal with LVM, RAID, scripting things, etc.
These days the cost of hard drives is so cheap that it might not be worth it, just get a few 1TB drives and use normal raid.
As suggested above though you could do something with LVM and expanding your VG over a newly added disk, but technically this wouldn't be "RAID". Remember that DROBO doesn't technically do "RAID", but they do something close with some proprietary methods.
You could get similar behavior to this picture by partitioning each drive into a series of RAID-5 components and putting them into LVM. If you add a new larger drive you would grow a bunch of the component RAID-5s.
Obviously, none of this would be automatic and I'm not sure that LVM Just Works if physical volumes grow under it.
