Very strange cache drive performance

[cinereus]

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.

[JorgeB]

BX500 is a value SSD without DRAM cache, not good for performance, the MX500 for example performs much better.

 

https://www.tomshardware.com/reviews/crucial-bx500-ssd,5377.html

 

[cinereus]

8 minutes ago, johnnie.black said:

BX500 is a value SSD without DRAM cache, not good for performance, the MX500 for example performs much better.

 

https://www.tomshardware.com/reviews/crucial-bx500-ssd,5377.html

 

Thanks. So are you saying this is normal and expected performance for the BX500? i.e. it can only cope with about 20GB at a time?

 

I realised that the Main tab shows very out of date temperature figures. Tested again using watch -n 5 'smartctl  -a  -d  ata  /dev/sdh | grep Temp' and can see after 45 it ramps up to 70C where the performance immediately drops to 0. Even after finishing the transfer, the temperature continues to rise for another 5-10 mins.

 

This means for every 20 GB to copy to the SSD you can't use it again for 10 full minutes!

[JorgeB]

Would expect a little better if it's being regularly trimmed, but not by much.

[cinereus]

Just now, johnnie.black said:

Would expect a little better if it's being regularly trimmed, but not by much.

So I'll get the same unusable performance with an ADATA SU650?

[JorgeB]

Don't know that model, look for some reviews, you want a 3D TLC based SSD with DRAM cache, like the MX500, 860 EVO, etc.

[cinereus]

On 5/13/2020 at 7:37 PM, JorgeB said:

Don't know that model, look for some reviews, you want a 3D TLC based SSD with DRAM cache, like the MX500, 860 EVO, etc.

Hmm, I just upgraded to a 860 EVO.

 

I'm still getting crazy throttling. It idles at 30 C and can crank out 1.6 GB/s for a few seconds. After a minute or so it reaches 35 C and speeds drop down to ~500 MB/s and after only about 100 GB written it's already at 43 C and speeds drop to <10 MB/s.

 

Is this normal for all SSDs to not be able to perform sustained writes?! 

[JorgeB]

10 minutes ago, cinereus said:

It idles at 30 C and can crank out 1.6 GB/s for a few seconds.

This is while the transfer is being cached to RAM, no SATA device can read/write at those speeds.

 

11 minutes ago, cinereus said:

After a minute or so it reaches 35 C and speeds drop down to ~500 MB/s

This would be the normal speed that device should sustain during writes.

 

11 minutes ago, cinereus said:

only about 100 GB written it's already at 43 C and speeds drop to <10 MB/s.

Doesn't look normal at all, also likely unrelated to temps, as 43C is nothing for an SSD during writes.

[cinereus]

I haven't been able to reproduce the very slow speeds yet but you can see the extent of thermal throttling for short bursts of writes here:

 

[JorgeB]

You're copying from/to the same device, that's not a good way to test.