iMac Pro iMac Pro: External USB 3 HDD speed drops severely after 5 minutes

[OBirder]

I use several external HDD drives for backup. The are connected via USB hub. I noticed extreme slow backups and went investigating.

I noticed that every time a backup starts it is with expected speeds (110/120 MB/sec). After 5 to 6 minutes I get an extreme drop in performance (10 to 20 MB/sec).

To isolate it I used the same drives and instead of connecting via USB hub, directly connect two drives to the iMac Pro. Approx. 6000 files with 83 GB. I used the exact same drives on my 2015 13" i5 MacBook Pro.

On the MacBook Pro the files copied in 16 minutes and didn't drop in speed.

On the iMac Pro the same takes over an hour longer.

Anyone explanation regarding the drop in speed? Could it be some settings (excluded them from Time Machine and Spot Light).

 

[bxs]

You don't mention the speed you got when connecting directly to the iMac Pro rather than via the USB hub. Are you saying the transfer took over an hour when connecting the drives directly to the iMac Pro ?

Are you using the same cable for both the MBP and the iMac Pro ?

When you say "backing up" is this with Time Machine doing the backup ? IF not, what are you using for backing up the data; Finder copy maybe ?

 

[mcaswell]

Not sure how helpful this will be, but I just did a test copy of about 45gb, from a Thunderbolt drive to a USB3 drive. The operation completed in about 10-11 minutes, speed was around 60-70MB/s. I did, however, notice one peculiarity. After about 5 minutes, the READ speed reported by iStat Menus for the Thunderbolt drive dropped to about 3-5MB/s, and stayed that way for about the next 3 minutes, before going back up to 60-70MB/s. The strange part was that even during this reported read speed drop, the WRITE speed on the USB3 drive continued to show 60-70MB/s and the Finder's time estimate did not grow. Also, the activity light for the Thunderbolt drive continued to flicker at about the same level during the reported speed drop as it did when the reported speed was normal. That leads me to believe that iStat Menu's indication of a read speed drop was not real.

Thunderbolt drive is the top one, USB3 on bottom... note the big drop in the Thunderbolt drive's read speed roughly halfway through, while the write speed of the USB3 drive remains fairly constant.

 

[OBirder]

You don't mention the speed you got when connecting directly to the iMac Pro rather than via the USB hub. Are you saying the transfer took over an hour when connecting the drives directly to the iMac Pro ?

Are you using the same cable for both the MBP and the iMac Pro ?

When you say "backing up" is this with Time Machine doing the backup ? IF not, what are you using for backing up the data; Finder copy maybe ?

I mirror my RAW photos from the main drive to external HDD's on a schedule. I keep 3 copies on 3 different drives. I came from Windows and used Bvckup. I tried on the Mac GoodSync and Syncovery.Both showed the slow down and I started to investigate.

For the test I just created a folder on one drive with all the files. I dragged it in a Finder window to the other drive. I had disconnected the 10 port USB hub and plugged both drives for the test direct into the iMac Pro (USB 3).

Did the same on the MacBook. Cables, power supplies and drives are the same.

Just did a test with my Samsung T5 connected to the TB3/USB C port and didn't experience the slow down. Seems only from USB to USB.

 

[mcaswell]

Hmmm... FWIW, I just repeated my test, this time from USB3 to USB3 (just a couple of off-the-BestBuy-shelf WD MyBook drives), and the 45GB copied straight through in about 11-12 minutes with no slowdowns, at about 60MB/s.

 

[Strelok]

Depends on what kind of files you are transferring. I have a ~100MB folder that takes longer to transfer than another that is about 4-5GB.

 

[OBirder]

Hmmm... FWIW, I just repeated my test, this time from USB3 to USB3 (just a couple of off-the-BestBuy-shelf WD MyBook drives), and the 45GB copied straight through in about 11-12 minutes with no slowdowns, at about 60MB/s.

Thanks for testing. By the way does iStat record the transfer rate over the full length? If yes, do you have link (I didn't see it in the AppStore)?

 

[mcaswell]

Not sure if it's on the app store, but their website is https://bjango.com (they make several similar apps... the one I use is iStat Menus, which shows stuff in the menubar and with drop-down menus). And yes, it will record a graph that shows the transfer speeds over a given period of time. The graph that appears in the dropdown menu looks to be maybe around 15 minutes worth, and then if you mouse-over it, it gives you other timespans (1 hour, 24 hours, 7 days, 30 days)... same with network and CPU usage.

 

[OBirder]

Not sure if it's on the app store, but their website is https://bjango.com (they make several similar apps... the one I use is iStat Menus, which shows stuff in the menubar and with drop-down menus). And yes, it will record a graph that shows the transfer speeds over a given period of time. The graph that appears in the dropdown menu looks to be maybe around 15 minutes worth, and then if you mouse-over it, it gives you other timespans (1 hour, 24 hours, 7 days, 30 days)... same with network and CPU usage.

Thanks, I may give it a try. It seems that 2 or 3 of the hard drives out of the 8 have that drop in performance. Just interesting that the same drive did well with the MacBook. But with this tool, I might be able to narrow it down to which drive is acting up and when.

 

[nambuccaheadsau]

What are you using to do the backups? For mine SuperDuper registered version is the fastest. I back up to an exterbnal Silicon Power SSD, general speed of the back up is around 350/370Mb/ps., and all done in under seven minutes, but then I am not heavily into music or photos. Are the external drives SSDs or platters?

I did have problems with my USB3 to an Hitachi SSD in a caddy. The problem was the USB3 cable. There are fake USB3 cables coming out of china hand over fist, even with some of the better brands.


https://community.ebay.com/t5/Shipp...FAKE-USB-3-0-CABLES-BEING-SOLD/qaq-p/22018512

 

[macsforever]

Not sure how helpful this will be, but I just did a test copy of about 45gb, from a Thunderbolt drive to a USB3 drive. The operation completed in about 10-11 minutes, speed was around 60-70MB/s. I did, however, notice one peculiarity. After about 5 minutes, the READ speed reported by iStat Menus for the Thunderbolt drive dropped to about 3-5MB/s, and stayed that way for about the next 3 minutes, before going back up to 60-70MB/s. The strange part was that even during this reported read speed drop, the WRITE speed on the USB3 drive continued to show 60-70MB/s and the Finder's time estimate did not grow. Also, the activity light for the Thunderbolt drive continued to flicker at about the same level during the reported speed drop as it did when the reported speed was normal. That leads me to believe that iStat Menu's indication of a read speed drop was not real.

View attachment 744802

Thunderbolt drive is the top one, USB3 on bottom... note the big drop in the Thunderbolt drive's read speed roughly halfway through, while the write speed of the USB3 drive remains fairly constant.

Buffer maybe?