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Extremely slow file transfer between networked Macs

I have a new Mac Pro, previous generation 2009 Mac Pro, and a 2012 Mac Mini all operating on an Airport Extreme (latest model, latest firmware) wireless network. The New Mac Pro and Mac Mini are running OS X El Capitan and the Older Mac Pro is running Yosemite. I am experiencing glacial file transfer speeds between the machines. I have even tried bypassing the wireless network altogether and connecting the machines directly to each other via ethernet, with wireless networking turned off, and the problem persists. I'm am trying to backup a large iPhoto library which is 290GB. When I try to copy the files to another machine, I get the "preparing to copy" message for about 5 minutes, then the files eventually begin to transfer, but extremely slowly (something like 1MB every 10 seconds.) Sometimes if I let the file transfer continue, it will speed up for a while, but it eventually slows down again. I know none of the disks are the problem since I've tried various combinations of machines and destination disks, and the problem is still there both in wireless and ethernet transfers. Strangely, I can download/ upload files form the internet at normal (fast) speeds; it's just computer to computer transfers that are lagging. I have searched dozens of posts but I have yet to find any solution to this issue. Any assistance would be greatly appreciated.

Mac Pro (Late 2013), OS X El Capitan (10.11.1)

Posted on Nov 6, 2015 7:35 AM

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8 replies

Mar 2, 2017 7:08 AM in response to Scott Frizzle1

Hi, did you ever find a solution to your problem?


I just took a 2009 Macbook Pro out of the closet to start using for a writing project (files hosted on my server, which is a Mac Mini) but for some reason the connection between the two computers is slooooooow (takes about a minute per megabyte transfer).


I have a few computers and they all transfer at full 1000mb/s ethernet speeds or 300mb/s over airport ("N"), but for some reason this old laptop won't do it. I would suspect the airport but internet speeds are blazing fast and the "Tx Rate" is about 200mb/s, which means technically speaking it should be grabbing files off the server at 25Mb/s, not 1Mb/m!


Laptop has El Capitan- Apple won't let me upgrade it to Sierra (El Cap is the last operating system allowed on a 2009 computer, without some kind of hack I guess). Would love to hear what your solution was if you found one.

Nov 6, 2015 11:35 AM in response to Scott Frizzle1

When did the problem start?

Upgrade to El Capo?

Change to the latest AE?


It can help to figure out when the problem started and what was done or changed in the network at the time that could cause it.


What is the full network setup?

ie.. What modem do you have? Is it also a router?

What mode is the AE running, bridge or router?


Open the Activity Monitor and give me an actual speed of the file transfer when it is computer to computer.. and then speed from internet.. I need actual numbers rather than just the description.. glacial.


I have even tried bypassing the wireless network altogether and connecting the machines directly to each other via ethernet, with wireless networking turned off, and the problem persists.

Am I reading this correctly.. you have run ethernet link between two computers directly, not via the Extreme.


If that is the case the issue is the computers and network setup. The extreme is exonerated.

It is really important to use SMB protocol now.. AFP is really slow.. I am not sure why but Apple have moved the default network to SMB since Mavericks and it does affect the links.


In each computer have you turned on SMB network shares.. If not please do so.


Or do it as a simple test in Extreme.. plug in a USB hard disk.. mount it in the computer using SMB from Finder, Go, Connect to Server in top menu area.

SMB://10.0.1.1 (replace with the actual IP of the Extreme).


Then check the file copy speed with a single very large file.. >1GB and report that number.


If it is still extremely slow..


What do you have IPv6 set to in the computers? It should be link-local only.


DId you do a NVRAM and SMC reset in the computers you upgraded to El Capo.. because network issues are not uncommon with upgrade installs.


How to Reset NVRAM on your Mac - Apple Support


Resetting the System Management Controller (SMC) on your Mac - Apple Support


If you don't have a backup of your important files and libraries .. I would suggest you get a large USB drive and plug it straight into the computer and directly backup the files.. there is always some danger in messing around that you do something that you will regret.. so backup beforehand by using a locally connected disk should still work fine.

Nov 21, 2015 3:00 PM in response to Scott Frizzle1

Hi Scott,


I'm noticing a similar issue with my MBP 2015 as well. When trying to copy files to either windows machines or another mac over my 5ghz wireless it's incredibly slow. It seems fine over 2.4Ghz but I have the same issue. If you have anything to note that could be helpful that you've figured out, I'd appreciate it. I have a feeling it has something to do with El Capitan. I do not remember having this issue prior to the upgrade. Thanks.

Nov 22, 2015 3:56 PM in response to ridergroov

If you upgrade installed el capo.. try doing the NVRAM and SMC reset if you haven't done so already.. I have posted the details above.


I would also clear out all the old wireless names in the computer.. then reboot it..


Rediscover the wireless and see if you get any improvement.


Your Mac must still be under warranty and if you have applecare ring apple support and get them working on the problem.. I am sure there are known problems with El Capo upgrades.. I clean install every OS now.. much less issues even if you have the migration of files and apps issues.

Nov 27, 2015 6:13 AM in response to LaPastenague

I have a similar problem to the OP and like him it appears not to be an Aiport problem so this thread might be in the wrong place.


I have 2011 Macbook Pro attempting to transfer a 100Gb Aperture library to my WD MyBook connected to Airport Extreme (early 2015?). Transferring smaller files such as 10 Gb video file and others, the speed appears acceptable but the aperture file takes an age to 'prepare', then slows right down after approx 300Mb transferred.


Ive tried direct connect to MacBook with USB but similar results.

Nov 27, 2015 12:46 PM in response to Nick W

Ive tried direct connect to MacBook with USB but similar results.

Your problem is not network.


If the disk is slow over USB you have something else happening.


Is the WD MyBook formatted Mac OS extended Journaled.. ie HFS+ ?? This is essential.. Aperture file will not copy correctly to FAT drive of any description.


I think you should reformat the MyBook drive (low level).. this might require you to download the tools from WD and I know how to do it on a PC but not a Mac.. many of the tools are DOS .. at least the better drive tests..


Disk utility is now a toy utility. El Capo has removed the heavy lifting side of it. But if you are running Aperture did you upgrade??


See if you have another disk to test on. But you should do a verify of the Aperture library.. again I am not sure if that is possible.. heavy slow downs are often a sign of corrupted file or disk.

Dec 5, 2015 12:14 PM in response to ridergroov

NVRAM reset is done completely separately to OS install..


I already gave the apple support document..


I gave exact details in this thread.


Re: My MacBookPro continually turns off the WiFi


Resetting of NVRAM will not harm the laptop and should be tried due to wrong values getting stored and that is the only way to clear them out.


(It is the same thing as a router reset.. you clear out flash which holds the current settings and returns to a standard setup.. this is often needed as things can be corrupted).

Extremely slow file transfer between networked Macs

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