Time Machine very slow after upgrade to El Capitan

My question is : is Apple about to do something about this problem which seems widely known even in the discussions here ?

What if anything Apple would be doing would be pure speculation. As such, this discussion forbids all speculation.

USB hard drives are actually slower than Firewire when it comes to USB 2. They are limited to several things:

1. The power of devices on their port.

2. The number of devices sharing the same bus.

3. The amount of data being shared on the bus.

Your System Profiler under the USB section can give you more information when you hook it up to each port. If you are seeing a slowdown, it is likely for one of those reasons. Also as a general rule of thumb, you don't want hard drives to become over 85% full, or your Time Machine backup drive to be less than twice the size of the original hard drive to avoid slowness.

These instructions must be carried out as an administrator. If you have only one user account, you are the administrator.

Launch the Console application in any of the following ways:

☞ Enter the first few letters of its name into a Spotlight search. Select it in the results (it should be at the top.)

☞ In the Finder, select Go ▹ Utilities from the menu bar, or press the key combination shift-command-U. The application is in the folder that opens.

☞ Open LaunchPad and start typing the name.

The title of the Console window should be All Messages. If it isn't, select

SYSTEM LOG QUERIES ▹ All Messages

from the log list on the left. If you don't see that list, select

View ▹ Show Log List

from the menu bar at the top of the screen.

In the top right corner of the Console window, there's a search box labeled Filter. Enter the word "Starting" (without the quotes.) You should now see log messages with the words "Starting * backup," where * represents any of the words "automatic," "manual," or "standard."

Each message in the log begins with the date and time when it was entered. Note the timestamp of the last "Starting" message that corresponds to the beginning of an abnormal backup. Now

CLEAR THE WORD "Starting" FROM THE TEXT FIELD

so that all messages are showing, and scroll back in the log to the time you noted. Select the messages timestamped from then until the end of the backup, or the end of the log if that's not clear. Copy them to the Clipboard by pressing the key combination command-C. Paste into a reply to this message by pressing command-V.

If all you see are messages that contain the word "Starting," you didn't clear the text field.

The log contains a vast amount of information, almost all of which is irrelevant to solving any particular problem. When posting a log extract, be selective. Don't post more than is requested.

Please don't indiscriminately dump thousands of lines from the log into this discussion.

Please don't post screenshots of log messages—post the text.

Some private information, such as your name, may appear in the log. Anonymize before posting.

When you post the log extract, you might see an error message on the web page: "You have included content in your post that is not permitted," or "The message contains invalid characters." That's a bug in the forum software. Please post the text on Pastebin, then post a link here to the page you created.

If you have an account on Pastebin, please don't select Private from the Paste Exposure menu on the page, because then no one but you will be able to see it.

Please read this whole message before doing anything.

This procedure is a diagnostic test. It’s unlikely to solve your problem. Don’t be disappointed when you find that nothing has changed after you complete it.

The purpose of the test is to determine whether the problem is caused by third-party software that loads automatically at startup or login, by a peripheral device, by a font conflict, or by corruption of the file system or of certain system caches.

Disconnect all wired peripherals except those needed for the test, and remove all aftermarket expansion cards, if applicable. Start up in safe mode and log in to the account with the problem.

Note: If FileVault is enabled in OS X 10.9 or earlier, or if a firmware password is set, or if the startup volume is a software RAID, you can’t do this. Ask for further instructions.

Safe mode is much slower to start up and run than normal, with limited graphics performance, and some things won’t work at all, including sound output and Wi-Fi on certain models. The next normal startup may also be somewhat slow.

The login screen appears even if you usually login automatically. You must know your login password in order to log in. If you’ve forgotten the password, you will need to reset it before you begin.

Test while in safe mode. Same problem?

After testing, restart as usual (not in safe mode) and verify that you still have the problem. Post the results of the test.

I don't think any more log extracts are needed. The question was whether Time Machine works better in safe mode.

You wrote earlier that the backups to the USB drive were taking hours. It seems now that they're running normally. The problem is the Time Capsule. How old is it?

I would need to see the log of an abnormal backup to the USB drive. Otherwise I can't suggest anything except to replace the Time Capsule. After six years, its hard drive is ready to fail, if it hasn't already done so.

I had the same problem and wasted a lot of time searching forums, only to find very complicated answers that were out of my league.
The incremental backup was 73Gb and it would take forever just to go up 0.1MB

With everything I've read, I came to the conclusion that it had to do with re-archiving the existing backup with lots of changes.

If my assumption was right, it left me 2 options:

a) Go on faith and delete the backup like some recommended. I was too afraid to do that...

b) Partition my drive in order to have a new destination where Time Machine could do a new Full backup while keeping the previous backup untouched on the other partition.

I went with b) and so far so good. I have to do a 262Gb backup while the previous one that took forever was 73Gb.

I just started approx 10 minutes ago and I'm at 8Gb. The transfer rate is good.

If it works, then I could go back and maybe remove the partition and do a)

The partition I did is only 400Gb out of a 1.5Tb drive. It's too small to keep a good history of TM.

UPDATE: This fresh new backup on the partition worked perfectly and went to 100% without any problems.

But I was still not ready to erase my full original backup and loose everything so here's what I did and it worked.

In Finder, I've opened the folder Backups.backupdb and started deleting some subfolders for dates in 2011-2012-2013. For those years, I kept only one each quarter (January, April, July, September and the last one of the year). Then for 2014, I kept one per month. For 2015, I kept them all.

Then I emptied the Trash which took overnight because it had over 3 000 000 items to delete.

I started the backup this morning around 8AM and left for work. It was doing this very long "Preparing Backup" when I left.

When I got back from work, the backup was done and it said it was done at 2h48pm. A reasonable time compared to the approximative 185 DAYS !!!! it was going to take originally at the speed it was doing the full backup.

Yeah, in my case, it was the virus scanning software that was causing the problem. I was using Sophos Anti-virus and Time Machine went into turbocharged mode once I disabled virus scanning on the backup disc. In fact, it is even better if you disable on-access scanning while the Time machine backup is in progress. It has backed-up 20Gb just while I've been writing this message. All good...