Problem: X-RAID vertical expansion - swapping in disk smaller than largest in array.
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).
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UPDATE: I read somewhere that unless the new swapped-in Hard Drive is not at least as large as the largest drive in the array, that vertical expansion will not be 100%. Something to do with X-RAID being composed of Raid-5 and Raid-1, which I did not undertand. So guessing I am toast and have to factory reset?
UPDATE: I read somewhere that unless the new swapped-in Hard Drive is not at least as large as the largest drive in the array, that vertical expansion will not be 100%. Something to do with X-RAID being composed of Raid-5 and Raid-1, which I did not undertand. So guessing I am toast and have to factory reset?
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Help! Please.
The limitations of OS-6 expansion are bit a complicated to explain, and have changed a bit over the years.
The general guidance has always been that the new drive either needs to be as large as the biggest drive in the array, or be the same size as the drive it replaces. It's actually a bit more complicated than that, but those rules are safe guidelines, and never result in sub-optimal space use.
When you expand vertically, the system does create multiple RAID groups that are concatenated together to give you a single volume. These RAID groups are also reflected in the physical partitions on the disks.
Let's assume that you
started with 6 TB drives in the NAS
with only 8, 10, and 18 TB sizes used later on,
and that your expansion followed all the rules,
just to help explain. (If that's not the history, your partitions will look different).
The mdxxx are the virtual disks associated with each RAID group.
md127 (6 x~6 TB) is all the sdX3 partitions, ~30 TB
md126 (5 x 2 TB) is all the sdX4 partitions, 8 TB
md125 (3 x 2 TB) is all the sdX5 partitions, 4 TB
md124 (2 x 8TB) is all the sdX6 partitions, 8 TB
These are all concatenated into your ~50 TB data volume.
When you replaced disk 3 (sdc) the system needs to create the missing partitions. It can create sdc4 and sdc5 with no problem, but there is not enough space to create sdc6 (it needs to be 8 TB, and your drive only has 6 TB left).
Going back to the layout grid, you end up with this:
You end up adding 2 TB to md126, and 2 TB to md125, but md124 can't be expanded.
The simplest solution is to exchange the 16 TB drive for an 18 TB model.
But if you are extremely careful, you can use the linux command line to shrink the sda6 and sdb6 partitions to 6 TB, and create a new 7th partition - ending up with this:
Going back to the layout grid, you end up with this:
Re: Problem: X-RAID vertical expansion - swapping in disk smaller than largest in array.
Thank you so much for your detailed explanation @StephenB
Very much appreciate your expert help on this.
I will do a factory default as the next step, since that is the simplest choice, once I finish with a lengthy backup. Hopefully that will solve the problem. But I really hate losing snapshots this way, and guessing there is no way to preserve them. They can of course not be copied, that I found out already.
I will do a factory default as the next step, since that is the simplest choice, once I finish with a lengthy backup. Hopefully that will solve the problem.
That will work, and give you the final partition table in my explanation.
Future upgrades of the smaller drives could then use 10 TB, 16 TB, or 18 TB sizes.
