Performance Comparisons – Client QD Weighted and TRIM Speed
Client QD Weighted
These results attempt to simplify things by focusing on what really matters – the Queue Depths that folks actually see when using these products. A dimension is eliminated from the previous charts by applying a weighted average to those results. The weights were derived from trace recordings of moderate to heavy workloads, which still ended up running closer to QD=1-2 even on a slower SATA SSD. The intent here is to distill the results into something for those wanting 'just the facts' to grab and go when making their purchasing decisions. Don't be alarmed by the low figures. Remember, these are low queue depths – the place where these SSDs actually operate when in use by those not just running benchmarks all day!
The 545S clearly shows here that despite the oddities noted earlier in this review, it performs well where it matters, with results coming close to match the 850 EVO.
Thanks to the plethora of data we have at our disposal from the new suite, I can derive some additional interesting data that nobody seems to have been paying any attention to yet. Have you ever deleted a large file and then noticed your system seem to hang for some time afterwards? Maybe file moves from your SSD seemed to take longer than expected?
That's your problem right there. In the above capture, a 16GB file was deleted while a minimal level of background IO was taking place. Note how that IO completely stalls for a few seconds shortly after the file was deleted? That's a bad thing. We don't want that, but to fix it, someone needs to measure it and point it out. Enter another aspect of our new testing:
Latency Percentile data was obtained while running a 'light' (1000 IOPS) workload in the background while files of varying sizes were deleted. The amount of latency added during the deletions was measured, compared with a baseline, and correlated with the sizes of the deleted files. The result is how much latency is added to the active workload per GB of file size that was deleted. In short, this is how long you may notice a stutter last after deleting a 1GB file.
The 545S turned in among the lowest latency penalties of any SATA part we have tested, and it's nearly as good as the 960 EVO! File deletions should have zero noticeable impact on performance here.
This is another result from a different set of data. While our suite runs, it issues a full drive TRIM several times. Some of those times it is done on an empty SSD, others is it done on a full SSD. Any difference in time taken is measured and calculated, normalizing to a response time per GB TRIMmed. In short, this is how long an otherwise idle SSD would hang upon receiving a TRIM command for a 1GB file. These times are shorter than the last chart because the SSD controller does not have to juggle this TRIM with background activity and can throw all of its resources at the request.
While the 545S did well on the prior test, something was clearly different here. Performing a full TRIM of the drive when full took well over a minute.