MP 1,1-5,1 Strange performance for OWC Mercury Electra 6G SSD

[gtackett]

I recently bought from OWC their Mercury Electra 6G SSD, installed it on their Accelsior S PCIe adapter card, and plugged that in to my MP5,1 in an empty 16x PCIe II slot.

I tried it out as a combined boot drive and data drive. Its performance was terrible.

So to try to understand why, I ran a few benchmarks. The most revealing one is probably this, from ATTO Disk Benchmark--

Although it manages to hit about 550 MB/sec read for a few sizes, and exceeds 400 MB/sec write for two transfer sizes, overall it's pretty bad. It's also hard to understand why the speeds aren't uniformly increasing (at least to some plateau) with transfer size.

Since that worked out so badly, I next tried installing the SSD in one of the MP5,1 SATA II drive bays.

That worked out much better, but still short of what I was hoping for, and still hard to understand why it performs the way it does--

At least here, read performance is more or less uniformly increasing, up to a plateau.

But it peaks out at less than 300 MB/sec, while when using the Accelsior S the peak is around 500 MB/sec (though only for a few transfer sizes.)

And write performance still goes all over the place. At 7 transfer sizes the write transfer rate is really bad.

I've been in touch with OWC's technical support, who apparently had no benchmark data for comparison but are looking in to why the SSD and the Accelsior S could be performing so strangely.

I also just warranty RMA'd the Accelsior S so they could compare mine with one of their own.

Maybe some of the very bright MacRumors audience can help with understanding this?

 

[dataid]

Check this writeup on Storage Review regarding the Samsung 860 QVO SSD.
https://www.storagereview.com/review/samsung-860-qvo-ssd-review

Compared to MLC or even TLC products, QLC-based SSDs have a very small continuous write ability. QLC SSDs mitigate this through adaptive SLC caching, but the short version of the story is after writing 10-15GB of data to the SSD at once, write speeds will drop from 1,500MB/s down to 100MB/s. Manufacturers see this drive instead working in burst activity, where users mostly read data from the drive, or write in chunks, allowing the drive to stay in the faster performance zone.

This may be relevant if the Original Equipment Manufacturer (OEM) for OWC is Samsung or the OWC drive uses QLC - based SSDs.

In the article look at the analysis, VDBench Workload Analysis, for Random Read 4K, Random Write 4K and Sequential Write 4K. You can see the effect at play for the two QVO Samsung drives compared to the other drives tested. See if the ATTO benchmark you are using has a similar testing mode and check your drive for this effect.