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Level 3

940 points

weirdly irregular throughput problem with two TCs

I've been mystified by a problem with weirdly inconsistent throughput (i.e. write/read speeds) involving my two time capsules, which consist of a third-gen 1TB unit and a fourth-gen 2TB unit. The 4th-gen is configured as a router connected via cat-6 cable to my cable modem, and the 3rd gen is configured in bridge mode and connected via cat-6 cable to the 4th gen. I have a MacBook Pro 15" (mid-2015) running OS X 10.11.5 which is connected via cat-6 cable to the 4th-gen TC. I've changed this cable, to no effect. I've upgraded the firmware on both TCs from 7.6.3 to 7.6.7 to no effect.

What I've observed in copying an ~1 GB file to and from each time capsule from the Finder desktop is that on the first try for each, throughput is good: from 30-50 MB/sec on the 3rd gen, and perhaps 50-75 MB/sec on the 4th gen unit. But if I try again (and on every subsequent try), throughput is *much* lower in each direction, ranging from 30 MB/sec down to about 7 MB/sec; this correlates with much longer times for the transfer to complete. I'm measuring throughput using the "Network" tab on the Activity Monitor app. Disconnecting the 3rd-gen unit has no effect.

Does anyone have an idea what might be causing the inconsistencies? I've checked, and during my tests neither Time Machine nor CrashPlan were backing up.

MacBook Pro with Retina display, OS X El Capitan (10.11)

Posted on May 27, 2016 11:05 AM

21 replies

odysseus Author

Level 3

940 points

May 30, 2016 5:07 AM in response to LaPastenague

Wow. I was trying to think of some configuration details that I didn't indicate, such as having FileVault2 enabled, or the built-in firewall. These could explain the asymmetry in throughput. Are you saying that the problem you've reproduced only involves El Cap, the third and fourth-gen TCs -- as long as they're not the 3TB model?

May 30, 2016 2:31 PM in response to odysseus

I have now reproduced the problem on both El Capitan and Yosemite.. for me Mavericks ran ok although the other poster said Mavericks also will slow down.. it just takes longer.

The asymmetry of the problem is really interesting.

In the screenshots I did i cut off the packet info from activity monitor.. that was a mistake.

I like to test with actually copying a file.. I changed the name of El Capo upgrade.. so 6GB folder and copied it to the TC and back again.

Start copying a large file or folder from the TC to the computer and watch the packet info from the activity monitor for network.. that might show some light on the problem.. a fix however is probably not going to happen.. but you can then compare it to the Gen 5 TC.

The problem is irrelevant to the disk size.. I have not yet checked on older TC but I suspect it will be the same.. firmware differences between models are fairly minor in terms of disk transfer. (All Gen1-Gen4 run the same basic processor and setup.. but different wireless cards and hard disk capacity).

odysseus Author

Level 3

940 points

May 31, 2016 9:50 AM in response to LaPastenague

I have not been able to reproduce the problem with the 5th gen Time Capsule: reads are about 60 MB/sec, and writes about 40 MB/sec. (which is the asymmetry one would expect).

I'm going to file a bug report with Apple about this.

Oh, one more thing: during my testing, I was dragging a file from the desktop to the root-level folder on the Time Capsule, and I actually experienced a kernel panic! 😟

May 31, 2016 2:34 PM in response to odysseus

I have not been able to reproduce the problem with the 5th gen Time Capsule: reads are about 60 MB/sec, and writes about 40 MB/sec. (which is the asymmetry one would expect).

Thanks.. that confirms that the issue is specific to earlier models.

I am still doing testing and the situation is not as simple as it seems.. Sometimes the Gen4 TC can run perfectly for hours.. then when I start checking things it will have issues.

Oh, one more thing: during my testing, I was dragging a file from the desktop to the root-level folder on the Time Capsule, and I actually experienced a kernel panic!

Was this to your earlier Gen or the Gen5?

Did you upgrade install El Capo on the computer?? If so please take the time to clean install the OS and migrate your user files and apps.

I have hardly any issues with OS having panic attacks by always clean installing. A small pain at the start for long term improvement in reliability.

odysseus Author

Level 3

940 points

May 31, 2016 2:43 PM in response to LaPastenague

LaPastenague wrote:

Thanks.. that confirms that the issue is specific to earlier models.

Was this to your earlier Gen or the Gen5?
It was to the 4th gen time capsule.
Did you upgrade install El Capo on the computer?? If so please take the time to clean install the OS and migrate your user files and apps. I have hardly any issues with OS having panic attacks by always clean installing. A small pain at the start for long term improvement in reliability.

This was my first kernel panic ever on this machine, which I configured with a completely clean install.

May 31, 2016 2:50 PM in response to odysseus

Painful when you do everything right.

You can go through the logs and see if you can find the cause of the panic. But I am far from expert in that area.

You would need to post in the OS X area or with your hardware.

weirdly irregular throughput problem with two TCs