Storage Pool free space after pool expansion

[frank2001]

A few days ago I expanded the capacity of the storage pool of my TS-853A, comprised of 5x3TB WD RED hard drives in RAID5, adding a 6th disk. The pool expansion operation went fine (it took about 18 hrs). and the pool capacity is now 13,6 TB. After that, I expanded the Volume to the max. capacity available. I ended up with:

- New Pool Capacity: 13,6 TB (Allocated 13,5 TB)
- Volume: 94,28% - 12,82 TB
- Snapshot guaranteed space: 5% - 696,26 GB
- Unallocated: 0,72% - 100,04 GB

Screenshot_2019-10-08 QNAP-TS-853A.png

From the Storage Pool Graph

Screenshot_2019-10-08 QNAP-TS-853A(1).png

you can see the Free Space is 0,1 TB and the subscription is 99,3%, not 100%

I tried again to expand the volume capacity but I always ended up with 100,04 GB of unallocated space and I'm not able to add that free space of the pool to the volume.
I'm not sure whether there was some unallocated space in the pool prior to the expansion, but if so surely it was no near to 100 GB otherwise I would have noticed it.
I wonder why I'm not able to reclaim this free space for the volume. Is it something to do with the snapshots?

[MrVideo]

While I do not know about your deal with the 100GB, I do have to ask why you are running a 6 drive RAID5? You are asking for trouble. I hope you are doing constant backups. If a drive fails and you lose another drive during the rebuild, your data is toast.

[frank2001]

While I do not know about your deal with the 100GB, I do have to ask why you are running a 6 drive RAID5? You are asking for trouble. I hope you are doing constant backups. If a drive fails and you lose another drive during the rebuild, your data is toast.

Merely for max. storage capacity. I started out with 4 disks and overtime added 2 more. How many disks would you suggest as maximun for a RAID 5?

[MrVideo]

Four disks. There are some users here that will put forth that once you get to three disks, to use RAID6. Especially when using the larger capacity drives (=> 6TB).

You've painted yourself into a corner. The only way to go to RAID6 now is to start over, especially if you decide to upgrade the drives to larger ones in the future.

[frank2001]

You've painted yourself into a corner. The only way to go to RAID6 now is to start over, especially if you decide to upgrade the drives to larger ones in the future.

What do you mean by "start over"? Execute a RAID migration from RAID5 to RAID6?

[dolbyman]

you can add an extra drive and convert raid5 to raid6

[frank2001]

you can add an extra drive and convert raid5 to raid6

Ok, thanks. That's what I supposed. Of course in that case I would have to ponder whether I would be better off by adding a larger extra drive for the RAID level migration and later on expand the pool replacing the current disks with new larger ones.

As to the original problem of my post, do you have any idea?

[storageman]

If you reduced or removed the guaranteed snapshot space you could have expanded the volume to a larger size.
Are you using snapshots, do you need 700GB?

[frank2001]

Yes I'm using snapshots but I could reduce the guaranteed snapshot space if that would help to reclaim the 100 GB free space for my volume.
Are saying those 100 GB of free space are related to snapshots though not clearly stated in the graph?

[storageman]

No saying that and not sure why you can expand with that 100GB.
Thin volume can give issues but yours is thick
Click the down arrow on storage pool to see if it changes,

[frank2001]

Just now, I've reduced the guaranteed snapshot space form 696 GB (5%) to 500 GB (3,59%). Then I have expanded the volume to max size gaining 196 GB, exactly the same amount freed from snapshot space. Still I have 100 GB unallocated in storage pool, so this has nothing to do with snapshots management.

Is there someone who has expanded the volume (thick) to max size of storage pool? Do you have some space unallocated?

[frank2001]

Oops. Just seen now your reply. If I click the down arrow on storage pool I see no change from before.

[storageman]

I presume you have backups.

It's odd, if you try to create another volume with that 100GB does it allow you?

If you know Putty you could try restarting the LVM. It may correct the space issue.
"/etc/init.d/init_lvm.sh"

[MrVideo]

What do you mean by "start over"? Execute a RAID migration from RAID5 to RAID6?

For some dumb reason I thought that you had filled your NAS with drives, but you have two slots left. So the suggestion to add another drive and migrate to RAID6 was the correct answer.

[frank2001]

It's odd, if you try to create another volume with that 100GB does it allow you?

Not a new thick volume. It says there is not enough space.

Instead I managed to create a new 100 GB thin volume.

Screenshot_2019-10-11 QNAP-TS-853A(1).png

For the moment I'll settle with it.