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How to do incremental vertical expansion in FlexRAID mode using SSH commands
So, Netgear only lets you do vertical expansion in FlexRAID if you replace all of the drives in the volume. I'm here to tell you that, as long as you are comfortable with the command line via SSH, yo...
Yes, there are some additional specifics about expansions I didn't cover. Thanks for adding that.
I started on the experiment of removng a drive and the whole thing locked up on a re-sync again. Wish I knew which drive was causing that. I'm starting over, but with a simpler system: 3x1TB RAID5 changing to 2x1TB RAID2 because I know the troublesome drive is one of the 2TB ones. From there, I can try going back to a single drive so the second can be added as RAID0 or JBOD. From what I've read, that second step is actually pretty straightforward since each drive contains all the data.
I've got the RAID sync'ed and am adding some data. So, unless it all crashes down on me again, I should have some results in a couple days.
See Reducing-RAID-size-removing-drives-WITHOUT-DATA-LOSS-is-possible for successful reduction experments.
I have done some additional testing and have found the following:
It is possible to concatenate all of the mdadm options in one command. The sync problem I had following doing so was definately a result of a failing drive. So # mdadm /dev/md126 --grow --level=5 --raid-devices=3 --add /dev/sdb4 would have worked with better drives.
It is possible to add more than one drive at a time to an existing RAID volume, so long as it already consists of two drives. You cannot add two drives to a single-drive RAID1 (which is what Netgear's single drive "JBOD" really is) and simultaneously convert it to RAID5.
You can (using --force) add one drive to a single-drive RAID1 and simultaneously convert it to a two-drive RAID5. This goes a lot faster than adding a drive and making it a two-drive RAID1. Of course, like a single-drive RAID1, a two-drive RAID5 is non-redundant. But the NAS will say the volume is healthy. I suspect that's fall-out from it calling a single-drive RAID1 (aka JBOD) volume healthy. But as long as you intend to add at least a third drive, it is a faster way to expand a single drive system to a three-drive RAID5 because you avoid the excruciatingly long sync for a single to two drive RAID1. [I have yet to figure out why that seems to take so much longer than other syncs.]
BTRFS always expands to fill a RAID group that you expand, assuming the BTRFS volume already includes that RAID group. I don't know if that's new in BTRFS and the articles I Googled are out of date or this is unique to the ReadyNAS and some process it runs in the background.
I have verified that it is possible to add multiple drives at once. But you must start with at least a 2-drive RAID1 when you do. So, adding partition three of two drives in slots 3 and 4 to an existing two-drive md127 RAID1 would require:
# mdadm /dev/md127 --grow --level=5 --raid-devices=4 --add /dev/sdc3 /dev/sdd3
I have also found that is is possible to grow a single-drive JBOB (really 1-drive RAID1) to a 2-drive RAID0. But, you have to do it in two steps. The following grows a single drive JBOD by adding partition three of a drive in slot 2:
# mdadm /dev/md127 --grow --level=0 # mdadm /dev/md127 --grow --raid-devices=2 --add /dev/sdb3
This will temporarilly change it to RAID4, do a sync, then change it to the desired RAID0.
If you are adding a drive (like the expansions above, or for any reason) rather than replacing one, it is difficult to set up the proper OS and swap partitions (fdisk doesn't like to start where md0 does on the ReadyNAS) and also to make sure that those partitions get synced with the others that make up the OS and swap RAIDs. The best way I found to do that is to use the GUI to tell the NAS to create a new volume on that drive, then DESTROY the volume (which you can do before it completes, if desired). You can then use cat /proc/mdstat to see the md0 and md1 syncs complete and then use fdisk to create the partition(s) you intend to add.
This ends my experiments. I've not touched on RAID6, RAID10, or RAID50, but I'm sure the process is pretty much the same, you just have to insure you have the correct minimum number of drives. If it refuses to do a conversion, you may need to break it into two steps, like for the RAID0 expansion above.
Thanks for posting this. My "spare" NAS are just 2-bay units, so there isn't a lot of experiments I can do.
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