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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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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. – Marnix A. van Ammers Jan 1 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 at 3:10
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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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    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 '20 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 at 3:07
  • what the heckko y r there 2 flags? – beatrixthecat Jan 1 at 5:15
  • Please take the tour to see how the site works. – nohillside Jan 1 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. – Marnix A. van Ammers Jan 1 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). – Marnix A. van Ammers Jan 1 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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