Network-based Time Machine frequent backup corruption
||Date Originated:||27 December 2013|
When Time Machine backup is used over the network (most notably wireless network), it prompts to remove the entire backup set and start from scratch at an interval of about every two weeks. This have been happening since the early days of Time Machine and hasn't been fixed as of 10.9.1.
Steps to Reproduce:
1. Setup Time Machine encrypted backup over a wireless network connection.
2. Keep it running every hour (as per normal Time Machine backup schedule) for about a month while actively using the computer.
3. Once in a while when Time Machine is currently running, disrupt network connection by turning off Wi-Fi or putting the machine to sleep and taking it outside wireless range.
Backups are supposed to be reliable – intermittent network connection may be an excuse to skip a few files from being backed up (which should get corrected in the next backup cycle), but not to corrupt the entire backup set.
Within a month you should experience a "Time Machine completed a verification of your backups on <backup host name>. To improve reliability, Time Machine must start a new backup for you". Then a full re-backup could easily take overnight, even on Gigabit ethernet (at least my 2011 MacBook Air with about 200GB data takes about that much time whenever this happens).
OS X 10.9.1 / Build 13B42
There have been claims of workarounds available around the Internet, but none of these are capable to eradicate the problem:
- Overriding the file permissions in the backup volume to be public-writable.
- Increasing the sparse disk image's band size: http://arzur.net/2010/08/31/time-machine-on-a-network-drive-you-will-need-to-increase-the-band-size/
Maybe you should switch to a better method than having a disk image mounted over the network. Failing that, you could try using a more robust file system for the remote disk image – a file system that could survive and recover from random disk corruptions (as what happens when you issue low-level disk commands over a wireless network connection).
This affects network backups on both 3rd party NAS and Apple's own Time Capsule, as per what the forum discussion thread linked below (and several others on the Internet) have shown.
Forum discussion: https://discussions.apple.com/message/21530110?ac_cid=tw123456#21530110?ac_cid=tw123456
Whereas the following is my specific configuration:
- MacBook Air 13" Mid 2011.
- OS X 10.9.1
- WD MyBook Live
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