Time Machine volume keeps corrupting

[diedrichg]

I actually now have a script that monitors the system log and initiates a snapshot whenever time machine completes a backup. I'm away right now but I'll get it posted as soon as possible.

I'd like to use your script. Would you post that here as well as a new thread, please.

 

[fracai]

No problem. Jonas had caused a few headaches, but I should get it posted today.

 

[Robert Trevellyan]

I've had Time Machine flake out with a simple USB hard drive

Same here, it's just a lot less frequent.

 

[fracai]

Here is the script that I'm using with TimeMachine. I've been using it successfully for quite a while without issue, but improvements and bugs are welcome. Feel free to file those on the main ZFS Rollup repo.

Edit: I've merged the TMSnap components in to the the main ZFS Rollup repo.

 

[grahamperrin]

… Time Machine verifies backups (is that what you call deep traversal), …

No, those two things are unrelated to each other.

The traversal is of a file system on the Mac, for data that may be not yet backed up. The traversal occurs:

• without a check of consistency of the HFS Plus file system; and
• without verification of integrity of the files.

The Apple-provided routine for verification of a Time Machine backup with network attached storage is, essentially, a sequence of two things:

1. a temporary copy of a fraction of the backup – of some metadata – from the NAS, to the Mac
2. at the Mac, using that copy, a limited check of file sytem consistency

– limited because with the fraction alone, no repair can be made.


Further reading (technical)

CopyHFSMeta in open source for OS X 10.11.2.

The OS X manual page for fsck_hfs(8).

In Ask Different:

• the accepted answer to What is the OS inside the Time Capsule?
• How to tell which files are entirely or partly within a band of a sparse bundle disk image? – I upvoted the answer, but I never found an opportunity to test (to mark the answer as accepted)

– a comparison of NetBSD (in the Apple products) with FreeNAS (based on FreeBSD) may observe that good use of FreeNAS can be better than what's possible with Apple's products. For example, where FreeNAS is used with ZFS and scrubbing:

• all data in a pool is examined to verify that it checksums correctly.

Perceptions

… as @grahamperrin pointed out, Time Machine over AFP is flaky regardless of the host platform.

Those were not my words. Some other people describe AFP as flaky.

Consider this possibility:

… a drop in network connectivity …

For fun: imagine a network cable, in a dusty corner of the room where my FreeNAS stuff is kept. That cable, severed – during a backup – by an escaped rabbit with anti-Apple tendencies. I assume that the AFP replay cache is not designed to make everything perfect after ungraceful interruptions at critical times.

There: AFP for Time Machine is neither perfect, nor flaky :)

 

[fracai]

Just a quick message to note that I've moved the TMSnap components in to the ZFS Rollup repo.

 

[Robert Trevellyan]

Those were not my words.

 

[grahamperrin]

@Robert Trevellyan it's OK :) sometimes I'm in/around conversations where people express overlapping concerns about mixtures of technologies.

With a clearer sense of each part of the mixture, it should be possible to improve the documentation for FreeNAS …