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I've installed a DIY nas box with ubuntu server (10.4) which runs on 4 2TB hard-drives in raid 5. On all 4 disks I've created a 300MB boot (ext3) and the remainder is raid. On top of this raid I've used LVM to create volumes for swap, root, var, data etc.
This works like a charm but I now have recoverable raid errors on the 1st drive so it needs to be replaced, the problem is that the box boots of this failing drive. Is is possible to move the /boot partition to an usb stick and boot from that? I'm a bit reluctant to do this all 'hot-swap' since it hosts around 5TB of my photos/music/movies with no real backup (..I know..).
I've already noticed during installation/testing that removing drives 'reorders' the /dev names which doesn't seem to be a real problem as raid/lvm seem to be looking for guid identifiers. So either I need to move/copy the /boot to one of the other drives but with every update I need to update those copies too so moving /boot to a usb stick seems the most logical option to me. I'm not sure if this can be done easily with raid/lvm/grub2 etc.
2nd question, I'm thinking of migrating the current 4 disk raid5 to a 6 disk raid6, would there be noticeable degradation in performance or is it about the same?
If the box (BIOS) supports USB booting, should be do-able. Don't know I'd like it as the only long-term option though.
What about mirroring that boot partition ?. That way you at least get 2 disks you can survive over without you having to remember to copy it. Would need the MBR on the second be written so that it pointed to itself (i.e. its own disk) rather than the original (failing in this case) disk.
Ubuntu typically uses UUID to locate filesystems, so booting from either disk should be seamless.
No experience with software RAID, but I can't imagine RAID6 would be a major performance hit - unless you have consistently high write loads, and the disks are sharing channels/busses. Even then wouldn't be much more than RAID5 I'd reckon. All conjecture on my part as I said.