When I first put up a storage box, it was built out of 4x 500GB disks, later on, I expanded to 1TB disks. What I did was partition the 1TB disks into 2x 500GB partitions, then create 2 RAID arrays: Each array out of partitions: md0: sda1, sdb1, sdc1, ...etc. md1: sda2, sdb2, sdc2, ...etc. All of those below LVM. This worked for a while, but when more 1TB disks started making way into the array, performance dropped because the disk had to read from 2 partitions on the same disk, and even worse: When a disk fail, both arrays were affected, and things only got nastier and worse with time. I would not recommend that you create arrays of partitions that rely on each other. I do find the JBOD -> Mirror approach suggested earlier to be convenient though. On Tue, Sep 22, 2009 at 3:58 PM, John Robinson <john.robinson@xxxxxxxxxxxxxxxx> wrote: > On 22/09/2009 12:52, Kristleifur Dađason wrote: >> >> On Tue, Sep 22, 2009 at 11:24 AM, Jon Hardcastle >> <jd_hardcastle@xxxxxxxxx> 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. > -- > To unsubscribe from this list: send the line "unsubscribe linux-raid" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- Majed B. -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
