Very slow Time Machine backups on 2015 MacBook Air

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Level 1

9 points

Very slow Time Machine backups on 2015 MacBook Air

Related to a discussion topic from a few days ago (Two MacBooks, 10.11.4, one quick TimeMachine backup and one very slow), I am starting a new topic with new information which appears to show it is a more general problem, and not related to network Time Machine.

Here is the situation:

A 2015 MacBook Air, 10.11.4, 8 GB/512 GB, has extremely slow Time Machine backup performance, taking 40 hours for the first backup of 300 GB and very long incremental backups as well
TM performance is essentially identical whether over the network (hardwired Ethernet) or to an external USB3 drive
When backing up to USB3 drive, I have confirmed that System Information shows that the port is configured as USB3, not USB2 (nothing else is plugged in to the USB port)
Raw I/O bandwidth tests (using dd and iperf) show no problem; network bandwidth reaches 110 MB/s, network writes run at 50+ MB/s, external HD USB3 writes run at 40-50 MB/s (hard drive write speed limit)
3 other Macs of varying ages from 2009 - 2014 on the same network have no issues at all doing network Time Machine backups; a full first backup on a 2011 MacBook Pro of 500 GB takes 5 hours, or more than 10x faster than the problem MBA
Network Time Machine uses a Linux server running the latest Debian and Netatalk 3.1.8, and the connection is through a USB3/Gigabit adapter, not WiFi, and iperf tests with this arrangement shows 900 Mb/s throughput to the server. In any case, network Time Machine and external USB HD Time Machine show the same symptoms.
The problem MacBook Air is as identically configured to the 2011 MacBook Pro, which it replaced as the "daily driver", as possible
This problem has been shown by this MBA since its unboxing, taking about 20 hours for its first backup after early configuration. Incrementals now take many hours, resulting in interrupted incrementals and, I believe, corrupted backup databases triggering new full backups which are now taking 40 hours.

Using Terminal and iostat, Console, etc., I see that on the MBA during TM backup there is substantial I/O activity to the backup drive on the order of 20-40 MB/s for sustained periods, but during that time the average reported backup size as reported on the TM window and in the console is growing by only 5 GB/hour. This occurs the same whether the backup is going to the external drive or network drive. This seems to mean that of all the I/O bandwidth to/from the external HD, only 1/600 contributes to the backup's progress. I'm certain there is overhead of some verification and other tasks, but not at a ratio of 600 to 1.

I tried disabling low-priority I/O throttling as outlined here: http://apple.stackexchange.com/questions/212537/time-machine-ridiculously-slow-a fter-el-capitan-upgrade, which helps a bit (maybe 20-30%), but not by a factor of 10 which others saw.

I have gone through a number of the steps in Pondini's Time Machine troubleshooting, but have found nothing there matching these symptoms.

The only thing I can conclude is that Time Machine, the application or its configuration, on this specific MBA, is broken. (One thought as I was writing this up that I have not tried: the MBA and the MBP both run VMware Fusion and have a 50+ GB VM file; on the MBA this is not excluded from TM backups while on the MBP it is)

Does anyone have any hints on what to look at next? In any case one key would be why it seems that only 0.16% of all the I/O bandwidth to/from the backup drive seems to be actual backup data.

Again, three other Macs, all running the same 10.11.4, back up to the network Time Machine server flawlessly and have for years. Only this brand new MBA sticks out as broken, whether to a network drive or an external USB3 HD.

MacBook Air, OS X El Capitan (10.11.4)

Posted on May 6, 2016 10:22 AM

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Answer 1

Eric Root

Level 10

684,039 points

May 6, 2016 11:34 AM in response to mklein9

(One thought as I was writing this up that I have not tried: the MBA and the MBP both run VMware Fusion and have a 50+ GB VM file; on the MBA this is not excluded from TM backups while on the MBP it is)

What happens when you exclude it like the MBP?

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Answer 2

mklein9 Author

Level 1

9 points

May 6, 2016 11:39 AM in response to Eric Root

I'll have to wait until I have access to it, tonight. But this wouldn't help with the slow first full backup.

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Answer 3

mklein9 Author

Level 1

9 points

May 9, 2016 9:32 AM in response to mklein9

I think I have solved this, but see the detail to determine whether it might work for you.

First of all, given the detailed experiments and data I had, I went to the local Apple Store Genius Bar and they rather quickly diagnosed it as a likely hardware problem related to the SSD. In the end, I walked out of the store with a new MacBook Air.

Came home, restored the new MBA from the one and only TM backup I'd ever gotten to finish in the last two months (on the external USB3 drive), which worked great. First order of business was to start a network TM backup. Initial 50 GB again went fast (about 1 GB/minute) and then started slowing down, approaching 5 GB/hour.

One of the things the Genius pointed out was if high CPU usage of mds_stores was identified, it could be a problem with the Spotlight indexing service. On a hunch, while TM backup was slowing down, I disabled Spotlight indexing on all volumes with the command:

sudo mdutil -a -i off

and pretty much immediately the backup rate came right back up to, and exceeded, the previous 1 GB/min rate. At this rate, after 4 hours the full backup, 280 GB, was done, and the first incremental after that took 2 minutes.

Afterwards I reenabled Spotlight, but only on the local drive, with:

sudo mdutil -i on /

It remains to be seen if this is a permanent fix or not, but it certainly brought the full initial TM backup time right into the range it should be, limited largely by server drive write bandwidth. In any case, Spotlight indexing network shares, at least in our case, should be considered carefully as it may be extremely flaky. See the post https://discussions.apple.com/thread/6499628?answerId=26520737022#26520737022.

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Answer 4

mklein9 Author

Level 1

9 points

May 9, 2016 9:42 AM in response to Eric Root

Eric, it turns out that the VM image was already excluded from backups. I am not sure why I thought it wasn't.

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Answer 5

Nov 16, 2016 5:05 AM in response to mklein9

I had a similar problem after recently adding a Synology 216J NAS and using this for Time Machine backups (as well as storing my music for Sonos).

I seem to have resolved it by deleting Avira antivirus software from my iMac. Instantly, the backups went from taking forever to only taking a few minutes. I read somewhere that someone else cured their problem by deleting Sophos, a similar type of software. Give it a try if you havre Avira!

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