Is there a good version of Time Machine?

Michael keybounce at gmail.com
Mon Feb 29 10:41:02 PST 2016


On 2016-02-29, at 3:35 AM, Ryan Schmidt <ryandesign at macports.org> wrote:

> Non-Apple implementations of AFP (i.e. netatalk) are simply not sufficiently compatible with Apple's implementation to work reliably with Time Machine, no matter what the third-party vendor trying to sell it to you says.

From what I understand, Apple's protocol was changed to permit signaling back to the originating machine when something was actually out on the disk, rather than just in the buffer. That's issue number one.

Issue number 2, of course, is data corruption. This was the big thing from previous years -- a network packet is checksummed over the wire, and goes into the network card buffer when correct. Then, it is transferred to the computer memory, possibly with error. Same thing, in theory, with the transfer inside the drive.

People who have done the math say that drives getting invalid data is not a question of "if", but of "how much".

> I learnt the hard way that TM's efficiency is not necessarily what you expect it to be. Corruption from power loss on an external drive three times, surprise corruption on Linux server running AFP 3.4-compatible Netatalk two times in 3 months.

Ok, lets see. You had power loss on an external drive, on a Linux system. So the Linux system was either reporting "file stored on drive" when it was not, or it is not a compatible version of AFP (running the older protocol that does not report file stored, *and Time Machine will not list those servers unless you force it to*).

As a side note: I figured out how to force Time Machine to do a full backup without destroying the past. Memory is that I added a recovery partition to the backup, did a backup; then, removed everything except the recovery partition, did a backup; then, put everything back, did a backup. TM did a full backup of everything. The result? I had two copies of everything that did not change, plus the copy-after-copy of things that did change. So, if something happened to clobber a file on the backup drive, there is another copy. Given the inevitable "data damage will happen", that's just prudent normal operator behavior.

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