Slow SSDs, why?

[geeksheikh]

Hi, I have several ssds that are to be added to an ssd pool. I did a perf test on them to see if I had any slow disks...and uhhh...it seems I have some VERY slow ssds. They start off writes around 500MB/s+ but then get down to 20MB/s or lower after a bit. I realize there is some slowdown expected but this is very slow and it's not across all disks. Some of my oldest, cheapest disks have no issue sustaining writes of over 100MB/s, any ideas?

 

Attached the full output and the script used to test the devices, along with a screenshot of the device IDs and models so you can see which drives are so slow.

 

Thanks for your thoughts.

ssd_perf_test.sh perf_results.txt

[JorgeB]

Most SSDs cannot sustain high write speed, though 20MB/s seems really low, but using dd to test may not always be reliable, try an actual copy test, with large files, if the same it's the device.

[geeksheikh]

Thanks. Yeah I just spun up 4 ssds in a zfs raid 0 and rsync’d a 175GB file. Average speed was 22.9MB/s.  crazy. Something seems wrong. The ssds are connected via E-Sas using the card below. This goes to a sas controller in an external enclosure over 2ft esas cables

 

Card

https://a.co/d/b7Y8gwM

 

External enclosure, inside of another box.

https://a.co/d/fOXyRY4

 

 

Edited June 15 by geeksheikh

[JorgeB]

Try with other 4, or just a single one, different model ideally, if you get the same it's probably not the SSDs.

[geeksheikh]

Gonna do some testing with the SAS connections. Perhaps I have a bad cable or rail or setup. Will double check. Here's a pretty telling story