I'm new to Unraid and setting up my first server currently. After adding two drives to my array and formatting them to XFS, I started transferring data to them from an unassigned drive which is connected to the server directly via SATA, which is formatted as NTFS. I don't have parity or a cache enabled and want to transfer around 18tb of data to the array.

For the transfer I used the native file manager and i am copying, not moving, them over. The problem is that the transfer speeds are very slow, almost always ranging between 20 and 50 MB/s, occasionally jumping up to around 180 MB/s for a few seconds. I know that my drives are all fully functional, as they've been running totally fine on the windows machine they were on before, with read and write speeds well over 150 MB/s.

So what is going on? Am I doing something wrong? I'd understand the slow write speeds if I had a parity disk, but that's not the case. There's also plenty of free memory, although my CPU seems to have suspiciously high usage.

I'd appreciate the help! I attached diagnostics and some screenshots for clarification.

 

 

mono-diagnostics-20250421-1316.zip

This shows the actual speed the drive is writing at:

 

 

Does that speed remain constant or does with go to zero sometimes?

4 minutes ago, JorgeB said:

This shows the actual speed the drive is writing at:

 

 

Does that speed remain constant or does with go to zero sometimes?

It does go to zero sometimes, but just for a few seconds. Then it picks back up to around 275 MB/s again. The amount of time this transfer is taking does not match that write speed sadly. The read speed from the source drive matches the reported transfer speed as well. I wonder what causes that difference?

 

16 minutes ago, nokiya said:

It does go to zero sometimes, but just for a few seconds.

This means your IO queue is overloaded (Data coming in is faster than writing speed, first data is buffered in RAM but after this is full, there is no way to continue. So it stalls, waits until the RAM is written out and then continues) This looks like repeating Waves, and it is normal.

Writing takes much more times, not for the physical transfer only, but after the file is complete, the directories need to be updated and rewritten too. This includes a lot of additional writes and stepping. The smaller the files are, the more it will slow you down.

Nothing you can do against it, be patient.

 

Edited April 21, 20251 yr by MAM59

4 hours ago, nokiya said:

although my CPU seems to have suspiciously high usage.

 

This is due to IOWait being represented in the CPU load. If you open the terminal and type in  

top

  you will see the statistic for "wa" higher than 1.0 seen here:

 

IOWait is basically CPU waiting on the disk to complete it's tasks before it can resume doing CPU things.

 

This is precisely why people use SSDs in their unraid systems in their cache pools (not part of the array) because you can write much faster to an SSD than an HDD.

 

Edited April 21, 20251 yr by MowMdown