Low and unstable transfer speeds


Feb 22, 2024
Hello. I am struggling with low and unstable transfer speeds. After transfer init everything seems normal (but still slow and a bit unstable). But after some time the speed drops to unusable numbers (less than 1Gb/s). Is this related to the current release of TrueNAS, or might be related to some system misconfiguration? The client sends mostly the data from pool1 to pool2, or from/to a USB 3.2 Gen2 SSD hard drive. I visited most of the threads and followed most of the solutions, but no luck at all.

Screenshot 2024-02-25 at 20.33.12.png

  • Pool1: 1x RAIDZ2 | 8 wide | 7.28 TiB (2x SSD / 6x HDD) SATA, no special VDEVs
  • Pool2: 1 x RAIDZ1 | 3 wide | 14.55 TiB
  • Pool datasets: Sync = OFF, Compression = GZIP, Record Size = 4M, Permissions = NFSv4/SMB, Restricted
  • SMB Service: Default settings
  • SMB Share: Default share settings
  • Network: Two 10GbE ports in the bridge (br1) + 1x 1GbE uplink port for LAN access
My current rig details are below.

Thank you for any advice!


Oct 29, 2016
the first thing that comes to mind is to check for SMR disks. you don't list your drive models, so you would have to check them yourself

Pool1: 1x RAIDZ2 | 8 wide | 7.28 TiB (2x SSD / 6x HDD) SATA,
why do you have mixed SSD/HDD? this is generally not a great idea. it'll work, but any raidz vdev is limited to the speed of its slowest device, and the pool limited to the speed of the slowest vdev. the SSDs are wasted here.

slowing down after a transfer starts is normal; the first part is ARC doing its job, the slowdown is ARC having to write to your pool because ARC transaction groups arent big enough for the file. the only time you generally wont see this is with all SSD pools, because the SSD's move the bottleneck to the network.

your pool cannot go much faster than 1Gb/s, the speed of the slowest device in the vdev. HDDs rarely go faster than 125MB/s, which is 1Gb/s.

as such, what you have observed here looks pretty normal to me for the hardware and topology you have. if you want faster, you will need to design it different.

also, raidz1 on drives over 2TB is highly discouraged. you have gone over that by like 7x.