Re: Full use of varying drive sizes?

[John Robinson <john.robinson@anonymous.org.uk>]

On 22/09/2009 12:52, Kristleifur Daðason wrote:
> On Tue, Sep 22, 2009 at 11:24 AM, Jon Hardcastle
> <jd_hardcastle@yahoo.com> wrote:
>> Hey guys,
>>
>> I have an array made of many drive sizes ranging from 500GB to 1TB and I appreciate that the array can only be a multiple of the smallest - I use the differing sizes as i just buy the best value drive at the time and hope that as i phase out the old drives I can '--grow' the array. That is all fine and dandy.
>>
>> But could someone tell me, did I dream that there might one day be support to allow you to actually use that unused space in the array? Because that would be awesome! (if a little hairy re: spare drives - have to be the size of the largest drive in the array atleast..?) I have 3x500GB 2x750GB 1x1TB so I have 1TB of completely unused space!
> 
> Here's a thought:
> Imaginary case: Say you have a 500, a 1000 and a 1500 GB drive. You
> could JBOD the 500 and the 1000 together and mirror that against the
> 1500GB.
> 
> Disclaimer:
> I don't know if it makes any sense to do this. I haven't seen this
> method mentioned before, IIRC. It may be too esoteric to get any
> press, or it may be simply stupid.

Sure you can do that. In Jon's case, a RAID-5 across all 6 discs using 
the first 500GB, leaving 2 x 250GB and 1x 500GB free. The 2 x 250GB 
could be JBOD'ed together and mirrored against the 500GB, giving another 
500GB of usable storage. The two md arrays can in turn be JBOD'ed or 
perhaps better LVM'ed together.

Another approach would be to have another RAID-5 across the 3 larger 
drives, again providing an additional 500GB of usable storage, this time 
leaving 1 x 250GB wasted, but available if another 1TB drive was added. 
I think this may be the approach Netgear's X-RAID 2 takes to using 
mixed-size discs: http://www.readynas.com/?p=656

Cheers,

John.
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