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Despite having a gigabit hardwired ethernet connection to my Macbook Air, when I have Time Machine backing up to an iMac also hardwired on the same switch in the same network, the transfer speed is often less then 1MB per second.

If/when I copy a file from the Air (Catalina 10.15.7) to my iMac (Mojave 10.14.6), I get a speed of about 65MB per second. As it is, it takes about a month to get the 1Tb disk in my Air backed up, all that time sitting there with a wired connection and doing little else. If I could get 65MB/sec with Time Machine, it would take less than 5 hours to backup that 1Tb disk.

The backup disk is a 5Tb portable USB drive connected to the server (my iMac running Mojave) and configured to "share as a Time Machine backup destination". Several Macs (High Sierra, Mojave, Catalina) are successfully (but slowly) backing up to it over WiFi.

How can I get the initial backup to go as fast as possible?

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5 Answers 5

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Time Machine is really poor at working over a network, and I’ve stopped doing this. The best way to run Time Machine now (macOS 11) is to give it a dedicated encrypted disk (which TM will reformat to APFS). The backups will be very fast and you will be hard pressed to notice them, but even backing up to an HFS+ local drive will be orders of magnitude faster than over your LAN.

(The reasons for this are somewhat opaque, but the backup process is very different when backing up over a network as your target is not a disk or even a network folder, but a sparse image file on the network and this makes, as you’ve seen, a huge difference. The behavior seems to have gotten worse in recent versions to the point where it’s just not worth it.)

Another option you might consider is to use a syncing tool to sync your data to a location on the target machine that is part of its regular backup. I’d do both, but then I’m a "three backups are the minimal starter set” sort of guy.

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  • I do also backup to local portable disks, but I like the idea of also having backups of all the macs to a single location. I'm familiar with rsync and have considered using it. If the slowness is due to use of a sparsebundle image, why doesn't TimeMachine just use a directory tree in a regular file system? Why does it choose to use a sparsebundle? No need to answer, I'm just thinking out loud. Jan 1, 2021 at 22:56
  • Thinking aloud can be useful. Why a sparsebundle? TM requires a Mac file system (HFS+ or APFS). The only way to guarantee that on all types of remote system is put the file system inside a bundle.
    – Gilby
    Jan 3, 2021 at 3:10
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    No way a sparseimage alone causes speeds to drop that dramatically. There's gotta be a different explanation.
    – JBis
    Jun 14, 2021 at 0:50
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If all else fails, try this command:

sudo sysctl debug.lowpri_throttle_enabled=0

This command essentially allows the Time Machine to use all resources available, which should theoretically speed up the backup. Make sure to revert to the default afterwards, or else subsequent background system operations may take too much resources and make your laptop very slow.

Alternatively, you may want to try another sharing protocol. If you have been using SMB, try AFP or NFS. Additionally, you can try sshfs: if you choose the fastest encryption algorithm, IIRC it should be faster than all other three protocols.

As other answers stated, Time Machine over a network is really slow. The best option is to use a hard drive directly attached to the MacBook Air.

If you still insist on backing up over a network, you can try iSCSI. However, this is not provided nor supported by Apple. There should be commercial software that allows you to set up a iSCSI server on your iMac and access the target on your MacBook Air. This allows you to access the block device on your iMac over the network, and you can treat it like an external disk directly attached to your MacBook.

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  • I could also write my own shell or peel script & use rsync as I’m familiar with those. But more than anything, I really would like to know what is going on with TimeMachine that makes it so slow when backing up over a (fast) network. Feb 12 at 0:06
  • @MarnixA.vanAmmers I would say that the key issue is latency. If you attach a disk directly, then you only have to deal with the drive's latency and the filesystem latency. However, if you back up over network, you have to deal with the drive's latency (of the server), the filesystem latency (of the server), the SMB protocol latency, the network latency, the sparsebundle latency, and finally the filesystem latency (of the client). Add background APFS snapshot pruning (very filesystem/metadata intensive), slow backup over network is normal.
    – Joy Jin
    Feb 13 at 10:12
  • Because I don't know if your speed is normal, you can try to diagnose where the issue is: you can try to benchmark the SMB mount read/write speed and latency; you can also try to benchmark the mounted .sparsebundle read/write speed and latency. The problem is probably due to these two extra layers, but if the read/write speed and latency is fine for these two tasks, maybe it's really Time Machine's fault.
    – Joy Jin
    Feb 13 at 10:15
  • My suggestion is to either use your own script or to try Carbon Copy Cloner, which have the same features of Time Machine but is more configurable and easier to diagnose. If CCC takes the same time as Time Machine (it actually uses rsync IIRC), you can know for sure it's not Time Machine's fault
    – Joy Jin
    Feb 13 at 10:16
  • I did try that command and it made no noticeable difference. Feb 14 at 19:43
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The first time you use Time Machine, set it up in the evening so that the initial backup can be done overnight.

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  • 3
    Instead of posting three different answers please use the edit functionality to integrate them all into one post. Also make sure that the answer actually addresses the issue described in the question.
    – nohillside
    Dec 31, 2020 at 22:21
  • Welcome to Ask Different. This is not a 'forum' that acts like a chat about the problem. I it's good to research the problem and if you have a good answer, post it with your research. As @nohillside states, improve one answer with an edit instead of just posting more 'answers'. Cheers!
    – bjbk
    Jan 1, 2021 at 3:07
  • what the heckko y r there 2 flags? Jan 1, 2021 at 5:15
  • Please take the tour to see how the site works.
    – nohillside
    Jan 1, 2021 at 7:28
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    As I said, the client and server are both hardwired via ethernet (and they are in the same room). Even so, it takes about a month for the initial backup of the 1Tb drive on my Mac Air. Jan 1, 2021 at 22:50
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If your backup disk is a Time Capsule, leave your Mac in the same room as the Time Capsule for the initial backup, or use an Ethernet cable to connect your Mac to one of the Ethernet ports on the Time Capsule.

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    The backup disk is an external 5Tb drive connected to my iMac. Backups to it work, they're just slow (~1Mb/sec). Jan 1, 2021 at 22:51
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Virus scanning software can make Time Machine backups very slow. If you use Norton AntiVirus or a similar product, try to exclude your backup disk from automatic scanning. Also make sure you are running the latest version of the virus scanning software.

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