Reading/writing to the spinning disk array (5400 rpm drives) I get pretty steady speeds of 160 MB/s.
I installed a Crucial BX500 cache drive to try and improve this. I see good results reading from the cache drive with speeds about 430 MB/s.
However, I have very odd results writing to the drive. It goes at full speed (~450 MB/s) for 45 seconds to a minute before dropping to 5 MB/s for 15 seconds, going up to 400 MB/s for 5 seconds then back down to 5 MB/s for even longer. In the end, the net speed over a 100 GB file is less than 50 MB/s or 3x slower than my 5400 rpm spinning drives!
I thought it was thermally throttling as the Main tab shows the temperature hitting 70 C after lots of writes. But this is not consistent at all and it still reads as ~50 C sometimes even when throttling heavily.
(Is the temeprature reading very delayed perhaps? What about the reads/writes on that tab?)
What's going on here? Clearly an SSD running at 5 MB/s is not remotely fit for purpose.