Last week I bought a new external drive 8T USB-3, initialized for Time Machine with Big Sur on my MBP 15. I need to backup ~834GB. The first backup has started five days ago and is still running, ~130GB remaining. Why is it so slow?
MacBook Pro 15″, macOS 11.1
hyperviper wrote:
USB-C. Notice that the first ~400GB required ~three hours. It seem to me that as the backup goes on it becomes slover. Also I suspect that the problem is related with the new APFS backup format.
It is not unusual for disk I/O to be faster on small transfers because the drive can buffer incoming data faster than it can be written. That might explain why you observed 400GByte/3 hours (~2GBytes/minute) but your short test achieved 1GByte in 5 seconds.
Check your cables (USB-x or ThunderBolt) and the data transfer rates claimed by the external disk for sustained transfers. Note that TB cables marketed by Apple are rated much faster than regular "USB-C" data cables supporting USB v4, and if you are using the USB-C charge cable supplied for charging a MacBook it might only achieve USB v2 data performance. About USB on Mac computers - Apple Support
hyperviper wrote:
USB-C. Notice that the first ~400GB required ~three hours. It seem to me that as the backup goes on it becomes slover. Also I suspect that the problem is related with the new APFS backup format.
It is not unusual for disk I/O to be faster on small transfers because the drive can buffer incoming data faster than it can be written. That might explain why you observed 400GByte/3 hours (~2GBytes/minute) but your short test achieved 1GByte in 5 seconds.
Check your cables (USB-x or ThunderBolt) and the data transfer rates claimed by the external disk for sustained transfers. Note that TB cables marketed by Apple are rated much faster than regular "USB-C" data cables supporting USB v4, and if you are using the USB-C charge cable supplied for charging a MacBook it might only achieve USB v2 data performance. About USB on Mac computers - Apple Support
@Branta_uk, tnx for the pointer. I'm using a usb-c to usb-3 adapter from Amazon (USB 3.1 Gen 1 -> up to 5Gbps) and the external disk (WD MyBook) uses its own ps and its own usb-3 cable. My MBP is a MacBook Pro (15-inch, 2017) with these ports:
Four Thunderbolt 3 (USB-C) ports with support for:
In this moment it's stuck at 785.61GB by almost 2 hours, really odd.
BTW, it seems that I'm not alone in facing TM issues with Big Sur:
https://discussions.apple.com/thread/252044887?page=1
I'll wait for a fix.
Be sure you are not trying to use the MacBook Pro Charge cable as if it were a real cable. It has only charge conductors and USB-2 pathways, suitable for keyboards and not much more.
Similarly, the USB-C port on the Apple MultiPort Adapter AV is a charge-only port.
In 13 hours backed up ~12GB...
How is it connected? Ethernet or USB-C?
USB-C. Notice that the first ~400GB required ~three hours. It seem to me that as the backup goes on it becomes slover. Also I suspect that the problem is related with the new APFS backup format.
In order to make a test I have just added a new volume APFS and copied 1GB file -> 5secs 😐
It seems that Big Sur 11.2 update solved the problem, it's now working as expected.
Tnx all for support!
👋
Time Machine backup on a new disk is very very slow with Big Sur
