Hey guys, I am trying to confirm a few things here.
First off I have a Mac Pro 5,1 running High Sierra. I am booting off of a Samsung SSD Ultra II via a PCIe adapter card and Trim is enabled.
I was getting about 100mb/s write speed and 350mb/s read with HFS+, and now I after upgrading to High Sierra and it switching the drive to APFS I am atleast getting write speeds in the low 300mb/s and read has remained about the same.
But I have seen where people are getting ridiculous speeds with M2 drives, 1000mb/s plus. Is that because those drives are just that much better? Or is something wrong with my system or configuration.
Let me know what you think.
Thanks
1) There is no Samsung SSD Ultra II. I suspect you are talking about SanDisk Ultra II
2) The max sequential speed limitation difference between 2.5 SATA III SSD and PCIe 3.0 x4 NVMe SSD is huge.
No matter how good the SSD is, SATA III connection limited the max sequential speed at ~500MB/s
On the other hand, those NVMe SSD now already had PCIe 3.0 x4 connection, which will be limited to about 3000MB/s. Effectively 6x faster than a single SATA III SSD can do.
Also, even though you has a 2.5" SATA SSD, it doesn't mean that you will automatically have 500MB/s in any situation.
One of the very big factor is the SSD spec. Those "up to 550MB/s" really literally means "up to", not always there. In fact, some seller mixed different capacity SSD together (all belongs to same series), and then claim that "these SSD can do up to 550MB/s...". But the fact may be only the highest capacity model can achieve that performance.
Another common miss concept is "random read / write performance" vs "sequential read / write performance".
As I emphasised, that ~500MB/s is the "max sequential" speed. For something like 4k random read QD1, the SSD may only able to deliver 30MB/s (interestingly, NVMe not much better than that, don't expect 6x faster in this area). However, this is almost the single most important factor that define the "system responsiveness".
For OS booting, operating, apps loading ,etc. It's the low latency from the SSD help most of the time, but not the sequential speed.
So, as long as your system is not acting like running with a HDD. 100-300MB/s read / write is the very very normal area that a SSD usually operating at.
Of course, in our case, the PCIe adapter itself can also create an extra bottleneck on the cMP if it can't provide the required bandwidth. e.g. Your SSD can perform 500MB/s, but the adaptor can only provide 350MB/s bandwidth, then obviously your max speed will be capped at 350MB/s.
But in any case, you shouldn't compare your SSD's sequential speed to a PCIe NVMe SSD. The are completely different. Just like comparing a car to a jet.
