My MacBook fan was roaring. Again. Time Capsule edition.

My MacBook fan was roaring. Again.

This time, however, activity monitor didn't show much going on. It wasn't a Flash ad running in another user account. I didn't have a print job stuck in the bowels of Apple's dysfunctional printing framework.

It had been doing it for weeks. Sluggish performance, slow fan pinup, then continuous running. Something was draining performance and making heat -- and it wasn't showing up in Activity Monitor.

Or, at least, it wasn't obvious in Activity Monitor. I did see something called fsck_hfs using up 10% or so CPU.

To make a long story short - the problem was a defective Time Capsule backup. My MacBook was running fsck_hfs, a utility that "verifies and repairs standard HFS and HFS+ file systems". When I saw this I thought there was something wrong with my system drive - but it tested out fine.

A SuperUser tip clued me in. My MacBook was trying to verify the integrity of my 150GB backup -- over a WiFi connection. This is a singularly ineffective strategy, it would have taken days to complete. The laptop never ran continuously for that long; and there is something about this process that makes a MacBook run hot [3]

If I'd known what to look [1] for I'd have seen something like this:

Except it would have shown 2-4%. It only got to 92% when I connected the laptop to my TC via wired ethernet. It got to 92% then stuck there. The backup was toast.

I then disconnected all users and tried deleting the .img file for my MacBook from TC. That failed because the Finder can't handle TB scale image files [2]. I then used AirPort Utility's very confusing Time Capsule UI to erase the entire drive and started the slow, painful, recreation of my backups.

My MacBook is quiet and responsive again, and fsck_hfs free.

That was painful.

Backup is an unsolved problem.

See also:

• My MacBook fan was roaring. Why? 5/2008.
• Obnoxious old Epson Scan bug: EPSON Scan cannot be started 2/2008
• OS X 10.5.5: CPU pegging with Firefox 9/2008.
• When Safari locks up - Kill Flash process
• iMac G5: fans running more often 10/2006
• osx - Why has my Mac been running fsck_hfs for two days now? - Super User - great discussion of this problem
• Time Machine. Backup failed with error...: Apple Support Communities 9/2008

[1] I wasn't so direct, instead I wandered about searching Console error messages. There I found:

search console for com.apple.backupd (all messages)

Attempting to mount network destination using URL: afp://;AUTH=No%20User%20Authent@Molly.local/Molly_Internal

Backup failed with error: 21

Error writing Time Machine Information file: /Volumes/Molly_Internal/Stanford_MacBook_0017f2f04828.sparsebundle/com.apple.TimeMachine.MachineID.plist

Error writing to backup log. NSFileHandleOperationException:*** -[NSConcreteFileHandle writeData:]: Input/output error

Event store UUIDs don't match for volume: Escanaba

While plumbing Console I discovered an unrelated error that distracted me for a while - a pile of errors like this:

Jul 20 18:27:55 localhost com.apple.launchd[1] (com.apple.SystemStarter): Failed to count the number of files in "/System/Library/StartupItems": No such file or directory

Googling on this one I discovered this is an old OS X bug, one some systems a routine update deleted this folder. I recreated it using terminal:

cd /System/Library

sudo mkdir StartupItems

That cleared up a bunch of Console error messages, but it didn't fix my real problem.

[2] Kind of amazing, but there you go. Apparently they can be deleted via terminal, but erasing through TC is safer. You can only erase the internal drive, if you want to erase a TC mounted external drive you need to move it to a Mac and erase it there.

[3] The MacBook runs hot whenever it does an 802.11n TC backup. I wonder how much of this is heat output from the WiFi/encryption systems.