Why is my external SSD so slow at writing?

Hi there,

I recently (a week or so back) purchased a Mac Mini M2 Pro and all has been fine with it so far. It's running an HP U32 4K monitor with no problems and all external peripherals (keyboard and mouse and so on) are working fine too.

I've just gone and bought an M2 NVME SSD (WD Blue SN570) and an external enclosure for the drive and connected it to the Mac Mini. This is where things go bad unfortunately :-(

The write speeds I was getting with the drive were utterly appalling so I initially thought there could either be something wrong with the drive or perhaps the enclosure. I didn't have another enclosure but borrowed one from a friend which definitely works fine. Put the WD drive into that and same thing, really slow write speed. I was about to return the drive when I tried reformatting it. It was formatted as APFS but I tried MacOS Journaled instead.

I 'thought' this had done something as when I tried to copy a file across it went really quickly so thought it was something to do with APFS however that doesn't seem to be the case. The reason being that any smaller files (around 130MB or so) copy across really quickly but higher file sizes (I tried one at around 500MB) take an absolute age to copy. I could literally copy 50 x 130MB files across in the time it takes the 500MB one to copy!

This has led me to thinking that the drive and enclosure are fine but there's something wrong with either the Mac Mini or Ventura?

I'm not too sure what else to do to test all of this to find out exactly what's going on though so if anyone has any thoughts possibly on what I can do to figure it all out then I'd definitely be all ears, thank you.

I want to use the drive for video files and as it is at the moment it's just not usable at all unfortunately :-(

As I say though it only appears to have a problem with files over a certain size. I'm not sure of the exact size but seems to slow down to an almost compete stop at around the 400-500MB file size for some reason.

From my very limited amount of testing I'm fairly certain this is just a write issue and not read because when I do manage to copy a large file across (which takes ages!) then copying it back across from the external drive to the Mac is really zippy. Only seems to be writing larger sized files to the drive which is an issue.

If anyone has any ideas on this as to either what might be causing it or what I can do to test or even fix this then I'd be really grateful of any advice given.

A little more information. I was testing the disk using Blackmagic Disk Speed Test and when the disk is formatted using APFS then Blackmagic hardly runs. It literally takes around a minute before it does anything and then shows as writing at under 40MB/s!

If I format the drive as MacOS Journaled then Blackmagic does its thing right away and I get around 900MB/s instead.

However if I say go to the Finder and try to copy a large file across (even now the drive is MacOS Journaled) then it slows right down again and only goes fast if copying smaller files across.

I also tried setting the disk as a cache disk for Screenflow (screen recording software) and that seems to me to work fine in that it writes the file to the disk continually and I end up with a really large file as you'd expect from a long screen recording.

So (and I could be completely wrong on this) it feels to me like there is something stopping larger files from being copied to the drive in the speeds that I should be able to expect of it but something like Screenflow is having no issues as it's saving in smaller increments I guess?

This is a real pain as I'm thinking that I'm going to have to return the drive and the enclosure because at the moment they're not really usable for what I need to do though I'm really not sure of what to purchase instead of them if this is either something to do with the Mac Mini or Ventura :-(

Also I've no idea if this means anything as I've not really ever looked into drives this much before as they've pretty much always just worked but when I check out the drive with the System Information app it is saying EFI File System is MS-DOS FAT32? Should it be saying that when I formatted it as MacOS Journaled or is that something completely different I'm seeing there and nothing to do with this?

I've gone into the System Information app to check what it reports the drive speed as and it is coming up as USB 3.1 and says Speed: Up to 10 Gb/s so it's not like it's somehow limited itself to USB 2 and it is definitely reporting as USB 3.

This really is a massive problem for me as I need a large drive to be able to save video files to it and this is completely unworkable as it is right now. I just copied a 1GB file to the drive and it took 1 minute 15 seconds which is highly worrying!! :-(

Any help with this would be greatly appreciated.

Many thanks,

Mark