On Mon, 7 May 2012 00:32:35 +0000 Garðar Arnarsson <gardar@xxxxxxxxxxx> wrote: > That's an excellent idea, I was going to add another disk for extra space > right after migrating to raid6. > > Just to be clear, I'll be running the normalize attribute just once to > straighten the array out right? Or will I have to do it for every extra > drive I add in the future? Just once. > > And what are the N+1 you mention in --raid-devices=N+1 By "N+1" I just meant "1 more than the number of devices currently in the array". If you have both new devices ready to go, you just do a single reshape operation that converts to RAID6 and adds more space. This does not need a backup file and is probably the best approach. If you currently have a 10-drive RAID5 and want a 12-drive RAID6, then mdadm --grow /dev/md0 --raid-devices=12 --level=6 is what you want. NeilBrown > > Thanks. > > > 2012/5/6 NeilBrown <neilb@xxxxxxx> > > > On Sun, 6 May 2012 10:17:52 +0000 Garðar Arnarsson <gardar@xxxxxxxxxxx> > > wrote: > > > > > My raid5 array has gotten a bit big, it's containing total 10 drives > > > right now (I started out with 3 drives). So I am going to convert it > > > to raid6 before it gets any bigger. > > > > > > I am doing a test-run on a virtual machine with virtual drives to see > > > that everything works flawlessly. > > > > > > When I tried to convert the array to raid6 I got a error message about > > > a missing backup-file > > > > > > mdadm --grow /dev/md0 --raid-devices=5 --level=6 > > > > > > mdadm level of /dev/md0 changed to raid6 > > > mdadm: /dev/md0: Cannot grow - need backup-file > > > mdadm: aborting level change > > > > > > I added the backup file and was able to convert the array successfully > > > after that. > > > > > > My question is, how big is this backup file going to be? My real raid > > > array consists of 2tb drives, will the backup file be as big as one > > > drive in the array, or will it just be few megabytes or gigabytes? > > > I'm asking because I'm wondering if I need to buy an extra hdd for the > > > backup file or if the backup file can just be on my OS hdd that has > > > around 100gb free. > > > > The backup file is a few megabytes. Around 16MB I think. > > > > However if you are likely to add another device in the not too distant > > future > > you can save yourself a bit of time. > > > > If you > > > > mdadm --grow /dev/md0 --level=6 --layout=preserve > > > > It will just make the new few a 'Q-block' device, containing the extra > > RAID6 > > 'parity' block for each stripe. This doesn't require any reshape or or any > > backup file and is a lot faster. All it requires is a normal recovery > > operation. > > > > Then when you later add another device you can > > > > mdadm --grow /dev/md0 --raid-devices=N+1 --layout=normalise > > > > This will convert from the Q-on-the-last-device layout to a more normal > > rotated-P-and-Q layout at the same time as adding extra space. > > > > NeilBrown > > > > >
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