External SSD Slowing Down within minutes?

bdbolin

macrumors member
Original poster
Nov 5, 2012
35
6
Hey all - I have a new Mac Mini setup with an external SSD that I boot and run the OS with.
It is setup with the AFPS file formatting.

I run tests with the Disk Speed test and get:
~700mb/s read/write (it's an NVME M.2 Drive in a USB-C Enclosure)

After about 20minutes running, it'll suddenly drop to ~170mb/s. Following that it seems to drop further and the whole system freezes up.

I have enabled Trim support via Terminal.

Suggestions? Ideas? Why the sudden drop? It doesn't seem thermal related as it happens if the drive is getting hot or is still cool.

Update:
  1. Posters were correct - drive gets 900mb/s read/write is accurate. This is due to limiting USB3.1 inside the enclosure.
  2. The 2000mb/s I mentioned below - accidentally was reading internal drive. LOL
  3. The slowdown was = to thermal throttling (since learned with more testing)
  4. Crashing stopped after reverting back to HFS+ from APFS
  5. Have learned TRIM support doesn't work over the USB in the enclosure anyways.
 
Last edited:

Sarpanch

macrumors member
Jan 12, 2013
84
67
SoCal
Based on your description, I imagine the SSD is overheating in the enclosure and throttling the speed to prevent damage. What enclosure and SSD are you using?
 
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bdbolin

macrumors member
Original poster
Nov 5, 2012
35
6
Yes, changed USB-C ports, same errors previously on APFS
The setup is:
960 EVO 1tb M.2 NVMe
Enclosure is USB 3.1:
https://www.amazon.ca/gp/product/B07JC2ZTNV/ref=ppx_yo_dt_b_asin_title_o02__o00_s00?ie=UTF8&psc=1


So update - I changed the file format from APFS to HFS+ and my read/write speeds are now 1300/2000mb/s - WAY QUICKER!

SO FAR it's stable and hasn't crashed or dropped once. Fingers crossed it was a file system issue...

Note it was crashing previously as both a booted drive or used simply as an external drive.
 
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Sarpanch

macrumors member
Jan 12, 2013
84
67
SoCal
Yes, changed USB-C ports, same errors previously on APFS
The setup is:
960 EVO 1tb M.2 NVMe
Enclosure is USB 3.1:
https://www.amazon.ca/gp/product/B07JC2ZTNV/ref=ppx_yo_dt_b_asin_title_o02__o00_s00?ie=UTF8&psc=1


So update - I changed the file format from APFS to HFS+ and my read/write speeds are now 1300/2000mb/s - WAY QUICKER!

SO FAR it's stable and hasn't crashed or dropped once. Fingers crossed it was a file system issue...

Note it was crashing previously as both a booted drive or used simply as an external drive.
Just that you know, 2000MBps is technically not possible in that enclosure. It is based on USB 3.1 Gen 2 that maxes out at 10Gbps. With USB overhead, these enclosures generally max out at around 950 - 1000 MBps. Your speed test software is possibly behaving erroneously with the file system.
 
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bdbolin

macrumors member
Original poster
Nov 5, 2012
35
6
Just that you know, 2000mbps is technically not possible in that enclosure. It is based on USB 3.1 Gen 2 that maxes out at 10Gbps. With USB overhead, these enclosures generally max out at around 950 - 1000 mbps. Your speed test software is possibly behaving erroneously with APFS file system.
See - that's what I thought too. The ~900mbps made sense previously, but right now with HFS+ file system it is getting 1300/2000mbps.

I'm going to have to continue testing stability - but so far HFS+ has fixed everything. Hasn't crashed yet.
 

Stephen.R

macrumors 68000
Nov 2, 2018
1,506
1,067
Thailand
but right now with HFS+ file system it is getting 1300/2000mbps.
No, it isnt. USB3.1Gen2 won’t carry data at that rate.

I’m confused why you’d use a slow(er) USB disk for boot when the Mini has a crazily fast drive internally?
[doublepost=1549859923][/doublepost]I should add - it’s interesting the issue “went away” with hfs+. I had similar symptoms with USB-C drives (sata and nvme) (which are going back for a refund) used for storage. I don’t think I tried hfs+, just encrypted and unencrypted APFS.

The conclusion of the local distributor was that the usb3.1g2 chip in the drives has some issues to be worked out as it’s relatively new. It’s possible the same thing causes the issues you’re seeing. When it’s a non boot drive did the disk just disconnect eventually?
 
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ursamaior

macrumors newbie
Feb 10, 2019
4
2
OP, a couple of things :
1) sorry for my poor english.
2) you cannot enable trim on an external SSD via USB. So, if your SSD it's not "brand new" or if it's "new" but you already have deleted from it a great amount of data (several hundred of GB), this may may be the origin of your issue.
3) Impossible. With a USB 3.1 Gen2 your speed (write/read) can be "only" 1GB/s
 

Fishrrman

macrumors P6
Feb 20, 2009
17,444
5,657
OP:

Is this a 2018 Mini that you're talking about?
Or an older one?

If it's a 2018, why aren't you booting from the internal blade SSD?
 

bdbolin

macrumors member
Original poster
Nov 5, 2012
35
6
OK - looks like Blackmagic Disk utility was reading the internal drive of the MBP I was testing on. LOL. It's back to the ~900/900 which makes sense.

Yea this is for the 2018 Mini and I was wanting to run everything external. I may just end up going with something like the X5 drive instead - I didn't realize that it was so difficult to use M.2 speeds in an enclosure these days without USB3.1 bottle necks.

So far the HFS file system seems to be stable. I'll leave it at this for now. Looks like the APFS was what was causing issues to start.
 

kensic

macrumors 6502
Jan 11, 2013
353
13
Just that you know, 2000MBps is technically not possible in that enclosure. It is based on USB 3.1 Gen 2 that maxes out at 10Gbps. With USB overhead, these enclosures generally max out at around 950 - 1000 MBps. Your speed test software is possibly behaving erroneously with the file system.
See - that's what I thought too. The ~900mbps made sense previously, but right now with HFS+ file system it is getting 1300/2000mbps.

I'm going to have to continue testing stability - but so far HFS+ has fixed everything. Hasn't crashed yet.
well the op is actually right.... he did say 2000Mbps OR 2Gbps (note the lower case b)

usb3.1 gen 2 has theorical speed of 10gigabit/sec ( 10Gbps ).

so therefore, something is still wrong, with that enclouser he should be getting around 8-9Gbps in real life cases.

remember 8 bit (small b) is 1 Byte (big B)

so you said 2000MBps, this equates to 16Gbps....which is more than usb3.1 gen2 speed.

everything is rated in bit format (small b)....thunderbolt 3 is 40 Gbps (still small b)
[doublepost=1549915843][/doublepost]so just be careful about the B and b.....when it comes to network speed rating they ALWAYS advertise it in "b" term.

however, when it comes to advertise harddrive speed, they always advertise it in "B" term.

for an EVO 8 NVME SSD rated about 3500MB/s read - 2500MB/s = 28,000Mbps / 20,000Mbps.

and thunderbolt is 40 Gbps or 40,000 Mbps.

hope this clears up everything!!!