Slow Write Speeds/Throttling on NVME Externals?

[3SQ Machine]

I'm now on my second NVME drive and this is getting annoying.

So here's the deal, while in the process of sending back an Oyen Digital Helix NVME drive because of slow writes I picked up a replacement 1TB new Micron X8, rated about 1000 read/writes. Connects through USB-C (which is also the thunderbolt port on my iMac).

After reformatting, initial blackmagic speed test showed 950/950. Good enough.

So I proceed to do my usual data moving. On my externals I keep (1) a bootable copy of the OS (just in case) and (2) all my Logic Pro X libraries and projects. I use two APFS Volumes each dedicated for the purpose.

So after installing Mojave, booting it up, doing Migration Assistant THREE times because it failed the first two, I finally get it up and running.

Blackmagic Speed Test showed after boot showed 650 reads and 80 writes. WTF HDD? Kept trying it again, same result.

Waited a few, and then sought to copy about 200 GB of audio/logic files. It really bogged down hard to HDD speeds. Blackmagic showed 80 writes again, then it bounced up a bit to 150, back down, then back up to 650. Reads were now stuck at 650 or so and not moving. But writes were all over the map which matched my experience showing the progress bar being very inconsistent. This was just copying from one volume of the drive to the other, so should be super quick, no?

So what's the deal with these NVME drives, are they really all cracked up as they're supposed to be? Folks getting CONSISTENT write speeds out of these things? Is it the iMac (mines a 2019)? I'm about ready to throw in the towel and go back to SATA.

 

[Banglazed]

Why are you using these low grade NVME drives? I would recommend at least the Samsung 970 EVO/EVO Plus with this enclosure that I’m nearly getting identical speed using USB-C/A

SSK Aluminum M.2 NVME SSD Enclosure Adapter, USB 3.1 Gen 2 (10 Gbps) to NGFF NVME PCI-E M-Key Solid State Drive External Enclosure (Fits only NVMe PCIe 2242/2260/2280) https://www.amazon.com/dp/B07MNFH1PX/ref=cm_sw_r_cp_api_i_7lY-DbRQ00E8R

 

[junkw]

Samsung ^^ or Sabrent 1TB Rocket NVMe 4.0 Gen4 PCIe

 

[Ifti]

NVMe drives get HOT. Many drives are designed to throttle when the temperatures increase. Even the Samsung X5 is designed to throttle with heat, and I've seen it reduce down to HDD speeds at some points with heavy renders. That's why many SSD drives have external heatsinks - take a look a the ThunderBlade V4, which is a RAID enabled drive containing 4 NVMe's - the outside is just a giant heatsink and the blades inside touch the top surface (with paste in between obviously) so the top does act as a complete heatsink. Ive never had it throttle with heavy use.

When it comes to portable drives its a little more difficult. The blade is in a small enclosure and passive cooling is more difficult, dependant upon the material used for the case etc.
The only drive with consistent high speed that I know of at the moment is the Glyph Atom Pro - if you are prepared to pay for it! Ive just received one so will be testing it for sure!

 

[shokunin]

This drive is probably not throttling due to heat but rather it's SLC cache is full and it's trying to offload to QLC nand and it can't keep up.

The Crucial X8 is a QLC (quad-level cell) NAND drive, which is meant for decent read speeds, but has slow write performance. To combat the poor write performance they add on fast SLC (single level cell) cache to provide great write speeds but only for a limited amount of gigabytes. Once you fill that up then it has no choice but to write to the slow QLC Nand.

Over time the drive will flush the SLC cache and write to QLC NAND as fast as it can. The drive will then provide fast write speeds until you fill the SLC cache back up.

 

[3SQ Machine]

This drive is probably not throttling due to heat but rather it's SLC cache is full and it's trying to offload to QLC nand and it can't keep up.

Great point I think you're right. Too bad these QLC drives are the same pricepoint as SATA (for example, the SATA-based Sandisk Extreme 1TB is $169 or so). On paper, seems a no-brainer to go for the theoretically faster read/writes but high writes can make QLC slower than molasses. I'm going to see if I can get the size of this SLC cache from Crucial so I can get a sense of whether this drive will do the job I need it to. I don't need insane writes, but definitely above 80! At this point, I'm leaning towards returning and going the enclosure/internal drive route above. Seems silly to overpay for speeds I won't get beyond the USB-C 10 gb/s bandwith but if that means more consistency it's a fair trade.