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Forum Discussion
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...
Thanks for posting. Have you tried reversing an expansion? The most common scenario here is someone adding their second disk, and expecting jbod or RAID-0 instead of RAID-1.
Sandshark wrote:
Now, this process also seems to allow you to expand a RAID6 with just two drives in a RAID1 layer or three in a RAID5.
Another option (which maintains dual redundancy) is three in RAID-1.
Sandshark wrote:
It should also allow you to expand by adding drives smaller than the largest in the system. Just create the partition(s) and add to an existing RAID group. XRAID won't let you do that.
If the partition size matchs the size of an existing RAID group that will work (and although Netgear doesn't say much about it, XRAID also will work in that case). For example, if you had 2x4TB, and later expanded it to 2x6TB then XRAID in OS 6 will actually accept a third 4 TB drive.
But if you had 2x6TB to begin with, you can'd add a 4 TB drive to that RAID group. You'd have to create a new group (on new drives).
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.
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