User profile for user: jg000
jg000 Author
User level: Level 1
4 points

Why is Migration Assistant slow when transferring a 200GB user account?

I transferred my user account and applications (~ 200GB).

Source: MacBook Pro 16" (2020 - Intel)

Target: MacBook Pro 16" (2025 - M4)

Both Macs at 15.3.1

Cable: thunderbolt 5 (backward compat 2 gens)

Reported negotiated speed: Thunderbolt 1711MB/s

Time to transfer: approx 3.5 hours.

That works out to ~ 16MB/s. (usb 2.0 speeds)


As near as I can tell so far, the xfer worked great -- mission accomplished. But there is nothing impressive about the speed.


I would like to learn if this slow speed is normal for MA. Or, if not, what may have been going on with my setup to result in a slow (by today's standards) speed. I will say up front that I had no special data sets with millions of small files or anything unusual like that. TIA


[Re-Titled by Moderator]

Posted on Feb 28, 2025 9:15 AM

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User profile for user: jg000
jg000 Author
User level: Level 1
4 points

Feb 28, 2025 2:23 PM in response to Grant Bennet-Alder

Actually Thunderbolt gens 3/4 can run 40Gbps full duplex. The older intel-based MBP I was copying from has Thunderbolt 3. The new MBPs of course have Thunderbolt 5 which can do 80Gbps (and up to 120Gbps in certain scenarios).


In any case, from a pure bandwidth perspective, I should have seen much more than 1711MB/s. But that's not my query: I want to know why Migration Assistant runs so slowly when the source and target computers are both decently fast MBPs with a decently fast interlink.

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User profile for user: MacTechFor30yrs
MacTechFor30yrs
User level: Level 1
8 points

Mar 3, 2025 6:18 AM in response to jg000

I am transferring 2TB of data from a M2 MacBook Air to a brand new M4 MacBook Pro 14", because the 2TB is full. I've tried airdrop, I've tried Target Disk Mode by sharing disk and I purchased a new Apple Thunderbolt 5 cable, I've tried transferring the data first to an external drive. ALL SLOWWWWW. I used to be able to do 1TB in under 5 hours in Target disk Mode. 2TB has taken me over 30 hours to transfer! This is horrible for a new machine that cost over 4k and I'm using a $80 Thunderbolt 5 cable. It was never this slow! I have been an Apple Tech for over 30 years and the transfer rate has been like this probably since 2018. Please fix this!

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Why is Migration Assistant slow when transferring a 200GB user account?

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