Very low read performance from DrivePool folders (40 MB/s) vs normal NTFS (500 MB/s)

[olo]

Edited it to be more structured:

 

Hi,

I'm seeing a very strange performance issue and can't figure out what's causing it.

Setup

• Windows 11
• StableBit DrivePool
• 6 × 4TB WD Red SA500 SSD
• No duplication enabled
• Pool is shared over SMB
• Plex Media Server reads media through the SMB share 

The problem

Any file that is inside DrivePool is limited to roughly 40–45 MB/s.

This happens:

• reading directly from the pool drive (e.g. P:\Movie.mkv)
• reading directly from the underlying disk's PoolPart... folder
• local reads
• SMB reads

However, if I move the exact same file outside the PoolPart folder onto the same SSD, performance immediately returns to normal.

Approximate speeds:

Location	Local	SMB
Same SSD, outside PoolPart	400–500 MB/s	120–140 MB/s
Same SSD, inside PoolPart	40–45 MB/s	40–45 MB/s

So the limitation appears to follow the DrivePool filesystem rather than the disk or SMB.

Things I've already tried

• Stopping the DrivePool service
• Performance mode
• Antivirus disabled
• Different SSDs
• Reading from the pool drive
• Reading directly from the PoolPart folder

The result is always around 40–45 MB/s.

Since the exact same SSD can deliver 500 MB/s outside the pool, this doesn't appear to be a hardware limitation.

Is there anything inside DrivePool that could cause this kind of throttling?

Any diagnostics I should collect?

[Christopher (Drashna)]

That's very odd, and you should definitely be seeing faster speeds. 

If you could, open a ticket at https://stablebit.com/Contact

Also, doing this: 

https://wiki.covecube.com/StableBit_DrivePool_2.x_Log_Collection

And then running the StableBit Troubleshooter, using the contact ID request number from the contact form:

StableBit Troubleshooter - Covecube - Wiki

[olo]

Thanks for the reply and for offering to investigate.

I did some more extensive troubleshooting and wanted to post the results in case it's useful.

It now appears that DrivePool itself was not the cause.

I isolated the issue by testing the exact same files in multiple ways:

• Older files stored in the pool consistently read at only ~38–50 MB/s when tested over SMB using dd with iflag=direct (bypassing the Linux page cache)
• A hard link to the same file was just as slow, confirming it wasn't related to the DrivePool path.
• Creating a new physical copy of the exact same file immediately increased read speed to ~140 MB/s (SMB)
• A brand new file (download) read at ~135-140 MB/s as well.
• Finally, I used DrivePool File Placement + Balance to move one of the slow files from one physical SSD to another. After the move, the exact same file immediately increased from ~48 MB/s to ~140 MB/s.

We also verified that the files were:

• not fragmented (single extent),
• not sparse,
• not NTFS compressed.

SMB configuration, signing, encryption and the network were also ruled out. 

The only consistent pattern is that older files are slow until they are rewritten or physically relocated, after which they become fast again.

My current theory is that this is related to SSD data retention / NAND refresh behavior rather than DrivePool itself. The system was powered off for roughly 8 months (we moved to new house and I never got the time), and rewriting the data appears to "refresh" it. Would have thought that WD RED (purchased end of 2024) shouldn't have this problem but that's the only thing I can think of. 

So I don't think there is actually a DrivePool issue here anymore.

Sorry to have wasted your time, hopefully this can help if anyone else runs inte similar symptoms.