I’m copying ~200GB of JPGs to a new SSD (Crucial BX500). I’m getting intermittent poor performance. Frequently the write rate drops below 10MB/s and the average response time exceeds 20 seconds. See attached image for context. What cause be causing that? (Should I have bought a Samsung instead? 
)
Edit: the SSD is half empty.
Check your windows event log. Anything weird in there like errors under system? Screenshots?
It could also be the drive has a fixed size SLC buffer that’s filling up and then it has to write directly to the slow tlc till it empties the slc buffer. Then once the slc buffer is empty it can continue using it
Some drives like the phison pcie4 can use up to half the drive as the write buffer. Very clever. Other drives have a fixed write buffer size, effectively.
Checking Windows event log. There are no errors since I began the copy. There are three disk errors from today (I have three physical disks). They occurred about when I awoke my PC from sleep, so probably nothing serious? I have attached a screenshot anyway.
There is a periodic nature to the poor performance so you could be right about the fixed-size SLC buffer. I didn’t expect the result to be so dramatic (20 second response time seems abnormal)! But if this is expected behaviour, not a big problem as it’s rare I stress the drives like this.
One way to confirm the slc issue is to time it and the manually pause the transfer for 1 minute about 5 seconds before the hiccup would have occured.
Then if when you unpause the transfer you don’t see the throttle it’s almost certainly the slc throttle in effect
The BX line is also DRAM-less as far as I know. Maybe that’s part of it, at least for the unresponsiveness.
Don’t know if Samsung even makes SSDs of that “class” but staying with Crucial, the MX500 is pretty much on par with Samsung in it’s price range. Both have a 5 year warranty as well.
So I write to the disk for 30 seconds, pause the copy for 10 minutes, then restart the copy. I’m thinking 10 minutes is enough time to process that buffer.
After seconds of restarting the copy the disk activity shoots to 100% and displays the high response time and low write speed. How strange.
If I pause the copy again, the 100% disk activity, high response time and low write speed persist for about another minute even with nothing copying. Finally, restarting the copy again after the disk activity has settled back to 0 triggers the slow state yet again after just 20 seconds.
I copied the data to a different SSD on the same machine (Samsung 850 Pro) for comparison and I see no weirdness there.
Could this behaviour still be an artefact of the buffer?
the fact that when you hit pause at the start of the stutter and it still stutters suggests its more on the software/driver side? that’s an interesting set of symptoms though.
can you try another sata port? maybe one far away from where the one you’re using now is?
device manager > view by connection… screenshot?
I didn’t consider the underlying technology of the drive when I purchased it, I just wanted a bit more SSD storage on-the-cheap. Maybe that back-fired slightly
I tried a different sata port, but got the same experience. I have 4 sata ports only and they’re all located in the part of the motherboard.
If you swapped around that drive and the 850 and the weird drive still acts weird it’s probsbly the drive. Different swap says cables also.
Sounding more like the drive buffer behavior though
I have managed to replicate similar behaviour on a nearby laptop. The laptop has the 480GB version of the Crucial BX500 which I fitted to replace a mechanical drive. The response time is an order of magnitude better but it looks similar to my problem.
(Windows on the laptop is falsely reporting the drive as Western Digital but I know it to be the Crucial BX500.)
I think I agree with you this is a drive-related bug/feature. I’m going to avoid these low cost Crucial SSDs in the future. Thanks for the support. Much appreciated.
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