TerraMaster Forum

Hello,

I am currently facing the problem that I am not sure how to handle slightly different drive sizes. SSDs don't all have the same size, and when you buy a 4 TB SSD you can't really know before how many bytes exactly of space it will have since all the manufacturers do it differently.

I bought 4 SSDs, each 4 TB, for use in my Terramaster NAS. They are from different manufacturers, and so far two of them have a size of 4.09 TB while two others have a size of 4.00 TB.

I started configuring my Terramaster F8 SSD Plus NAS by installing one 4.00 TB SSD, so there it created the TRAID storage pool. Then I added one 4.09 TB SSD and extended the storage pool to use that as well. Then I added another 4.09 TB SSD, and after that finished, I added the remaining 4.00 TB SSD. So I have a TRAID storage pool with 12 TB size (I only use 7 TB of it so far though).

But now I want to buy a 5th 4 TB SSD and want to install that to move from TRAID to TRAID+ for double redundancy. But as far as I understand, this now won't work because of this:

To migrate from TRAID to TRAID+, your array must meet the following requirements: It must have at least three disks of the largest capacity.

viewtopic.php?t=6404

I do not have three disks of the largest capacity, since I have two times 4.00 TB and two times 4.09 TB. So to do the migration, I would need to have three disks of 4.09 TB size and then add another disk of 4.09 TB size? So I would have to buy TWO more disks to be able to move from TRAID to TRAID+?

But the new 4 TB SSD I want to get will be another 4.00 TB SSD, so I need to make it work with 4.00 TB SSDs. The SSDs that I know are 4.09 TB are not currently sold here any more. So all the new SSDs I will buy from now on will likely be 4.00 TB SSDs, not 4.09 TB SSDs. Eventually, I want to fill all 8 slots in the NAS with 4 TB SSDs.

So is there any way how I can edit my existing storage pool so that the two 4.09 TB SSDs I have are made smaller to be only 4.00 TB? I really don't need the 0.09 TB of space, I just want them to be used as 4.00 TB SSDs by the Terramaster Software. It should just remove those extra 0.09 TB. Actually, if these small size differences cause such major headaches, why is the Terramaster Software not automatically clamping a drive of 4.09 TB to 4.00 TB size to make sure it does not cause issues? It should be very easy for the Terramaster Software to do that so that no one has issues with it and it just works out of the box.

Sorry, we are currently unable to reduce the storage pool.
But we will discuss with the product team whether we can find ways to prevent this situation.

TMzethar wrote: ↑16 Dec 2025, 23:23 Sorry, we are currently unable to reduce the storage pool.
But we will discuss with the product team whether we can find ways to prevent this situation.

Thanks!

It also seems to be quite dangerous as in that it even prevents me from being able to repair my TRAID pool if one of my 4 TB drives dies? Because if the 4 TB drive that dies is a 4.09 TB drive, and I buy a new 4 TB drive that is only 4.00 TB, then it's impossible for me to repair the TRAID with that new drive, correct? Because if a 4.09 TB drive dies, I need to find a new 4.09 TB drive to be able to replace it? But if all the 4 TB drives that are available at that time then have only 4.00 TB, I'm stuck forever with a degraded TRAID pool that I can no repair, other than maybe with buying a 8 TB drive but 8 TB SSDs are very expensive so I'd like to never have to buy one of those. Is my understanding here correct?

And this issue does not exist if I would use regular RAID5 or RAID6 instead of TRAID/TRAID+, correct? Because regular RAID5/RAID6 would always just ignore the extra 0.09 TB space? So if I have a mix of 4.00 and 4.09 TB drives in RAID5/6, and then one 4.09 TB drive dies, I could replace it with a 4.00 TB drive without issues, right?

So the only solution I have for now to prevent issues in the future is to save my data somewhere, completely delete my TRAID pool and create a new RAID5/RAID6 pool that does not have these issues of TRAID/TRAID+? Is that correct?

Your understanding of the capacity issue is correct. However, RAID 5/6 and TRAID/TRAID+ are no different in this regard. Regardless of which RAID type you intend to rebuild, during the rebuild process, they will automatically use your smallest 4TB drive as the baseline. This means you won't have this problem next time you need to replace or add SSDs.

TMzethar wrote: ↑17 Dec 2025, 09:20 However, RAID 5/6 and TRAID/TRAID+ are no different in this regard. Regardless of which RAID type you intend to rebuild, during the rebuild process, they will automatically use your smallest 4TB drive as the baseline.

I don't understand what you are saying here? As far as I understand, with TRAID if I replace a broken disk with a new disk, the new disk has to have at least the same size as the broken disk. So I can not replace a broken 4.09 TB disk with a new 4.00 TB disk in TRAID. I have actually tested this today, I removed one 4.09 TB disk from my NAS and replaced it with a 4.00 TB disk, and I do not get the option to start the storage pool rebuild. It only gives me the option to create a completely new storage pool from the 4.00 TB disk. And I assume this has to be because replacing a 4.09 TB disk with a 4.00 TB disk is fundamentally impossible in TRAID?

But if my pool would be RAID5 made up of the same mix of 4.00 TB and 4.09 TB disks instead, then it would ignore the extra 0.09 TB and I could replace a 4.09 TB disk with a 4.00 TB disk. For RAID5, only the size of the smallest disk in the pool matters, and I understand in RAID5 all disks are considered the smallest size.

So there is a difference between RAID5 and TRAID here, and that's why I don't understand you say "RAID 5/6 and TRAID/TRAID+ are no different in this regard"?

Whether it is RAID 5/6 or TRAID/TRAID+, when the minimum capacity for creating a RAID for the first time is 4.09T, disks with a capacity less than 4.09T cannot be used to join the RAID, nor can they be used to replace and repair the RAID.

TMzethar wrote: ↑17 Dec 2025, 09:38 Whether it is RAID 5/6 or TRAID/TRAID+, when the minimum capacity for creating a RAID for the first time is 4.09T, disks with a capacity less than 4.09T cannot be used to join the RAID, nor can they be used to replace and repair the RAID.

I do understand that, yes. If I would start with 4.09 TB, then it would be the same issue in TRAID and RAID5.

But I did not start with 4.09 TB: I started creating the pool with 4.00 TB. So that is the baseline capacity in my case. But then I added 4.09 TB disks to the pool, and that creates the issue that I can never replace those with 4.00 TB disks in TRAID.

While in RAID5, if I create the pool the same with 4.00 TB, then add 4.09 TB disks, then I can still later replace the 4.09 TB disks with 4.00 TB disks without issues, right?

I guess you want to replace 4.09T with 4T? If at least two of your four SSDs are 4.09T drives, the extra 0.9T will automatically be combined into a 0.09T RAID1/5. When you try to repair or replace the 4.09T with 4T, the capacity is insufficient to repair the 0.09T RAID1/5, so it cannot be used for repair.
Indeed, when using RAID 5/6, this situation does not occur because the extra capacity is always discarded.

TMzethar wrote: ↑17 Dec 2025, 09:49 I guess you want to replace 4.09T with 4T? If at least two of your four SSDs are 4.09T drives, the extra 0.9T will automatically be combined into a 0.09T RAID1. When you try to repair or replace the 4.09T with 4T, the capacity is insufficient to repair the 0.09T RAID1, so it cannot be used for repair.

Yes exactly, that is my problem. I would need a way to "delete" the internally hidden 0.09 TB RAID1 it somehow automatically created when I expanded my TRAID pool with 4.09 TB drives.

TMzethar wrote: ↑17 Dec 2025, 09:49 Indeed, when using RAID 5/6, this situation does not occur because the extra capacity is always discarded.

Ok, then my understanding there is correct, thanks! So I think RAID5/6 is much safer then compared to TRAID/TRAID+, because with RAID5/6 I can easily expand or replace an existing SSD with a new 4 TB SSD without having to care if it is 4.00 TB or 4.09 TB. Maybe some other drives would be 4.10 TB or 4.11 TB and with TRAID I would always live in fear then that I can't replace them if they break, because I would always have to be able to find a new drive with the same exact size again, which is much harder than simply finding a new drive that is "at least 4.00 TB".

Then what I will do for now is create a new RAID5 storage pool where I mix 4.00 TB and 4.09 TB drives, and move over my volume from the TRAID storage pool to the RAId5 storage pool.

But I hope that in the future your engineers can work on an update for TRAID/TRAID+ so that it becomes just as easy to use as regular RAID5/6 for this case of mixing multiple 4 TB SSDs with very slightly different sizes from different manufacturers. It should be possible to simply make TRAID ignore something like those extra 0.09 TB and not make them "automatically be combined into a 0.09T RAID1" that is impossible to ever remove again from the TRAID storage pool.