I recently bought a couple of Samsung 1T EVO 970 SSDs to do some work:
basically I need to simulate the loading of a fairly big mysql database
(>80G). I'm currently hitting a very weird problem.

The mysql is percona 5.7. I attach the disk via USB3, partition it,
create an ext4 fs on one of the partitions, mount it, create a
directory on it, configure mysql to use it as the datadir, and then
initialise it for mysql use. All good so far. I then start the mysql
dataload, and it's progressing happily. 

Then the mysql server bombs out, and messages like the following appear
in the dmesg output:

[19718.093317] sd 12:0:0:0: [sdf] tag#21 FAILED Result: hostbyte=DID_OK driverbyte=DRIVER_SENSE cmd_age=27s
[19718.093327] sd 12:0:0:0: [sdf] tag#21 Sense Key : Illegal Request [current]
[19718.093330] sd 12:0:0:0: [sdf] tag#21 Add. Sense: Invalid command operation code
[19718.093333] sd 12:0:0:0: [sdf] tag#21 CDB: Synchronize Cache(10) 35 00 00 00 00 00 00 00 00 00
[19718.093340] blk_update_request: critical target error, dev sdf, sector 0 op 0x1:(WRITE) flags 0x800 phys_seg 0 prio class 0

I'm trying to decide whether I'm just dealing with a borked SSD (it
came from Amazon: yeah, I know - if I will buy SSDs from that source,
what do I expect?) - or something more subtle and/or complex. Reading
the above messages literally, they seem to indicate that a command is
being sent to the SSD and it's not understanding it.

Any thoughts would be most gratefully welcomed.