Thank you for the response.. >> Does Linux MD RAID support a method of hot replacing a disk WITHOUT >> having to resort to degraded mode? > > > Yes, it does, if you use a recent kernel + mdadm I remembered reading about this once, and researching once before, but I am pretty sure my Xubuntu 13.10 distro doesn't have the flavor of mdadm I need. (Awesome work on this tool Neil! With mdadm you have transformed the utility of the md subsystem, and made it almost impossible to break an array with bad options) > > However, you have another option anyway. Just remove the hot spare, > re-partition as needed, then grow the raid5 to raid6. > 1) Wait for the re-sync to complete > 2) Drop another old drive from the array > 3) Re-partition > 4) Add back to the array and re-sync > You will never have worse redundancy than current during the above process. > Personally, I'd probably use the hot spare to move to RAID6, and then use > the migration to move a drive to its replacement (assuming you have another > spare drive available). Thanks for pointing out that obvious solution, I had almost forgot! I think this had crossed my mind at some point, but I wasn't sure if I needed RAID6 at this time. The 2TB Samsung F4EG drives have a 1e^15 BER, which is on par with enterprise drives. I've been using them for about 3 years, and they are still barely audible and perform great. I have even purchased several used (The genuine Samsung article, Made in Korea, not the post-merger Seagate flavor) and they all seem to behave awesome. The other kink to this solution is that I only plan to have 4 drives in the system when all is said and done. I might just go with a RAID10 in that case. If I decide to go this route, migrating to RAID6 is certainly a great solution. > > >> However, in my situation, my RAID5 partitions start in the middle of >> the drive, complicating that slightly... Fortunately, I have a spare >> drive or two to assist. >> 1) Stop RAID array >> 2) Clone one of the RAID devices to a larger disk (Using dd) >> 3) Remove the old RAID device from the system >> 4) Restart the RAID array in readonly mode (to test that the clone was >> successful without marking the array as dirty, otherwise, revert to >> the removed disk) >> 5) Optional: Restart the RAID array in readwrite mode to confirm >> 6) Repeat 1-5 for each additional disk >> 7) Grow the array (Resync starts at the new space) >> 8) Grow the filesystem > I did start this process and migrated the first drive. Array downtime was acceptable to me.. Details: 1) I stopped the RAID array 2) I created a partition on my spare drive (starting at sector 2048 so my 4K sector drive lies on a 4K boundary) 3) I cloned the partition with dd, It ran for a few hours at 100MB/min sustained: dd if=/dev/sda2 of=/dev/sdf1 bs=1M (in another terminal: "while killall -USR1 dd; do sleep 60; done" was pretty handy for monitoring progress) 4) I couldn't figure out how to start the array readonly, but I assembled it manually with the following: mdadm --assemble /dev/md5 /dev/sdf1 /dev/sdb2 /dev/sdc2 /dev/sdd2 /dev/sde2 --no-degraded mdadm: /dev/md5 has been started with 5 drives. So, while this solution does require a spare disk, this is an option for migrating raid5 without running the array in degraded mode. > > Actually, I was trying to find the URL to show the migrate options, but > couldn't seem to find any docs in the mdadm wiki at: > http://vger.kernel.org/vger-lists.html#linux-raid > Also, the debian raid wiki, the Neil Brown blog, and various other > resources. Hopefully someone else will be able to provide the relevant link. > Perhaps searching the mailing list itself would be best (I definitely recall > seeing it discussed here), but I'm out of time now. Good luck. I recall seeing it at one point too.. Maybe it was in the btrfs man pages? Thanks again! -- 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
