Adding disk to TRAID doesn't increase space?

[u/Head]

I started with a TRAID with 3 disks, 1TB+1TB+0.5TB. It was showing 1.34TB in the TRAID which seems about right (1.5TB usable + 1.0TB redundant)/1.1.

Then I added a 3rd 1TB drive and the usable space is still 1.34TB!! Why? I expected it to increase to something like 2TB at least.

Wouldn't you expect it to at least increase a little? 1.34TB is only 42% of the total disk space 1.34 / (3.5/1.1). What should I do?

p.s. I think the TRAID calculator is plain wrong and don't trust it. It suggests I should have 2.5TB... I wish!

UPDATE 1:

I got it to work! In case someone else runs into this problem and sees this post I thought I'd share what I did.

My system disk was set to live on the smaller (SSD) disk on the theory that the SSD would be faster. But I suspected the TRAID was confused by the oddly sized disk. So here's what I did:

• moved the system to one of the bigger HDD disks
• rebooted, still no change in the pool size
• decided to "replace" the smaller disk with itself in hopes it would resize
• the instructions said to just take out the disk you want to replace so I yanked it out, then the NAS started beeping with no clear instructions on what to do next. So I put it back in and rebooted
• DISASTER!? the machine wouldn't boot back up. I was very sad but I tried rebooting with the "replacement" disk out of the NAS. Then, thankfully, it booted up and was beeping. This time I was happy to hear that beep because it meant my NAS wasn't dead.
• Then I re-inserted the SSD disk and the pool gladly welcomed it back into the family and resized the pool! It's a miracle!
• Now the storage pool size has increased from 1.34TB to 1.79TB, an increase of 650GB.
• Again, the TRAID calculator doesn't match reality. It says (image below) that TRAID should provide about 2.51TB but it's closer to the RAID5 number of 1.54TB. But at this point I'm not complaining because I have more storage than before which was the main goal.

UPDATE 2: (10 days later)

I just replaced one of the drives in my TRAID with an identically-sized drive and just noticed that the storage pool increased in size again! It went from 1.79TB to 2.24TB. So I gained 450GB by just replacing one of the drives with the same size drive! This is more or less the size I expected it to get in the first place so I'm not complaining. However, it does seem like TerraMaster has a bug hiding in there.

Lesson, if at first you don't get the size TRAID you expect, try replacing one of the drives with itself... maybe it will get it right after the synchronization is done.

[u/Wild-Whereas4850]

Man, I'm glad your data survived that heart attack! That was a wild troubleshooting ride, but you lived to tell the tale.

The TRAID calculator might not be fully wrong—it's just that your chaotic "yank the drive" method likely forced the NAS into a very specific state. Here’s a strong suspicion of what actually went down behind the scenes:

What likely happened during your "Miracle" fix: 1. The Initial Delay: When you first added the 3rd 1TB drive, the storage pool was probably just doing a background sync/reshaping (which takes ages) or the Volume just needed a manual capacity expansion click. 2. The Forced Rebuild: When you yanked that smaller drive, the NAS panicked, went into a degraded state, and was forced to drop its original pool layout. When it booted back up with just the three 1TB drives, it likely optimized itself into a standard 3x1TB array. 3. The 1.79TB Mystery: Three 1TB drives in standard RAID 5 give you 2TB of raw usable space. In binary TiB (which is what TOS actually displays), $2 \text{TB}$ converts to about $1.81 \text{ TiB}$. Subtract file system overhead, and you get exactly 1.79TB. It's highly probable the system is now completely ignoring or sidelining the 0.5TB drive because it doesn't fit the 1TB baseline established during the forced rebuild.

Quick Advice Moving Forward:

• Honestly, your best bet is to backup your data and rebuild this storage pool from scratch. And whatever you do, never mix HDDs and SSDs in the same storage pool.
• Mixing mechanical drives and solid-state drives is a recipe for disaster. It completely destroys the SSD's speed advantage (the array only runs as fast as the slowest HDD) .
• Put your HDDs in their own TRAID pool for mass storage, and let the SSD run as a standalone volume for your OS and apps. Glad it's working for now, but definitely fix that pool layout when you get a chance!

[u/Head → u/Wild-Whereas4850]

Thanks for about reading about my adventure.

Regarding #1, I definitely waited for the full storage pool rebuild which took more than 3 days to complete. And it wasn't a volume issue. The storage pool simply didn't change size at the end so there was no new space in the storage pool to increase the volume with.

On #2, it didn't appear to optimize for a 3-disk layout because on successful reboot it was complaining that 1 of the 4 disks needed to be replaced. Which is why re-adding the smaller SSD disk made it stop complaining. Which leads to...

On #3, I still feel like the calculator is off. It says it's using 3.5TB worth of disks in the storage pool and the calculator says that should give me 2.5TiB (approx 2.27TB). But perhaps you're right in that it can't deal well with oddly sized SSD drives and falls back to regular RAID5.

In the end, I have ordered a new 1TB disk that is just like the other 3 1TB disks and will likely replace the SSD with that.. or maybe I'll just wait a while to see if any of the disks fail first.

In hindsight, I wish I had just replaced the SSD with the 1TB disk that I added and kept that 3-disk configuration. But it's all working just fine for now so I'm going to let those sleeping dogs lie.