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Forum Discussion
Problem expanding X-RAID volume
I am running the lastest OS 6.10.8 on a 6-bay NetGear NAS.
I have a problem with vertical expansion. It is not giving me the extra capacity I calculated it should be giviing me.
BEFORE:
6 drives:
18TB
18TB
6TB
8TB
8TB
10TB
-------------------
Useful capacity about 44TiB (Base 2)
- RAID Space with RAID 5 [base 10]: 50000.000 GB = 50.000 TB
- Final Useable/Filesystem Size with RAID 5 [base 2]: 45512.697 GiB = 44.446 TiB (approx.)
- Protection/Parity Size with RAID 5 [base 10]: 18000.000 GB = 18.000 TB
AFTER DRIVE SWAP:
6 drives:
18TB
18TB
16TB
8TB
8TB
10TB
-----------------------------
Useful capacity about 49TiB (Base 2)
According to the popular web 3rd party calculator for NetGear, I should be seeing 53.35 TiB :
- RAID Space with RAID 5 [base 10]: 60000.000 GB = 60.000 TB
- Final Useable/Filesystem Size with RAID 5 [base 2]: 54639.659 GiB = 53.359 TiB (approx.)
- Protection/Parity Size with RAID 5 [base 10]: 18000.000 GB = 18.000 TB
But I am missing space. Why? I added an extra 10TB (=16TB-6TB) to the array.
Looks like the volume only expanded vertically about 5TB
What happened to the extra missing 5TB (or about 4.35TiB)?
Netgear's own capacity calculator is so old that it only goes up to 12 TB drives. So not useful.
The maching chugged for 4 days, resynched, then resynched again and the volume increased from 44 to 49Tib. It did NOT say it was expanding the volume, it just showed it was resynching for second time. But it was actually expanding the volume, just not saying it was and not expanding enough.
I am left to wait for your help. Or I have to factory reset, which I really hate to do. Backing up and restoring that much data is a nightmare, and I lose all my snapshots (snapshot space set at 100GB limit).
Help! Please.
2 Replies
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You are losing 6TB of the 16TB drive because it has nothing with which to RAID. Assuming the 10TB was added before the 18TB, the first 10TB could RAID with the 8TBs and 10TB, but the remaining 6TB cannot raid with the remaining 8TB of the 18TBs because they don't have a partition the right size. When you swap in a drive, it can only be the same size as another drive used at some point and at least as large as the replaced drive or larger than all, or you end up with unusable space. To use all the space, I believe you have to destroy and re-create the volume. I don't believe swapping out one of the smaller drives with another 16TB will work, but they do seem to have made some changes to how XRAID expands and I've not investigated that. Alternately, return the 16TB and get another 18TB.
Here is some detail, assuming you added the 10TB before the 18TB:
You have one RAID5 group of 6TB on all drives, or if you didn't start with 6TB drives, this is more than one smaller layer adding up to 6TB on each.
You had one RAID5 group of an additional 2TB on the 8TB, 10TB, and 18TB drives. That layer could expand to the 16TB.
You have one more RAID5 group of an additional 2TB on the 10 and 18TB drives. That layer could also expand to the 16TB.
Then you have one 8TB RAID1 layer on the 18TB drives. That's too big for the remaining 6TB of the 16TB drive to sync with, so that 6TB remains unused.
Had you put in the 16TB before the second 18TB, then there would be a 6TB layer on the 16 and 18TBs and another 2TB layer on the 18TBs, so all would be used.
Theoretically, another 16TB would have a 6TB that could RAID with the currently unused 6TB of the first 16TB drive. But that would create a 6TB RAID1 layer on just those two drives and be an "odd man out" for any future expansion, so I don't think it's allowed. It also still wouldn't create a volume the size you'd get with re-creation since the top 8TB of the 18TB are in RAID1 as would be the top 6TB of the 16TB's. With re-creation, there would be a 6TB RAID5 across the 16 and 18TB's and a RAID1 of just the top 2TB of the 18TBs.
A safe rule for expansion is to add a drive that is at least as large as the biggest drive currently in the array (not an intermediate size drive as you did).
There are a couple of scenarios where an intermediate size drive will expand correctly, but yours wasn't one of them.
The only way to get the extra 6 TB now is to do a factory reset, build the NAS, and restore all the files from backup.
If you can exchange the disk with the seller for a an 18 TB model, that would be a simpler solutoin.
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