23 Oct 2016

How to Improve Time Machine on the Mac

Time Machine, if you don't know, is macOS's built-in backup software. It just works, with zero or minimum configuration. Not only does it make it easy to backup data, but it makes it easy to restore, via its Finder integration. When it came out a decade back, it was impressively and beautiful, in fact, magical.

Fast forward to today. There are some things it could do better.

First, Time Machine backups are not bootable. They should be. I recently had a problem with my Mac [1] — the keyboard stopped working. I had to boot from an external drive to see if the keyboard would work there, in which case it might just be the internal installation of macOS that's corrupt. Unfortunately, I didn't have one, so I had to painstakingly create one. Time Machine backups should be bootable. Like a bootable clone, which apps like SuperDuper create.

Second, you shouldn't have to have an external disc to back up your files. macOS should use the free space on your hard disc to store earlier versions of files. I'm writing this on a machine that has 600 GB of free space. That can store a lot of backups of my valuable data. This type of backups won't protect against hard disc failure, filesystem corruption, or someone stealing your Mac. But it does protect against accidental deletion and overwriting. Like using Save As and accidentally overwriting the wrong file. Or an app messing up your data, like iTunes broken duplicate detection deleting a lot of my music that weren't actually duplicates. The filesystem should store older snapshots of files and entire directories, deleting them only when the disk runs out of space [2] [3].

Third, some desktop Macs have Fusion Drive, which combines a big hard disc with a small SSD to give you the best of both worlds: the size of the hard disc, and the speed of the SSD. If you have a Fusion Drive, macOS should back up data on the SSD to the hard disc, if there's sufficient free space. That way, if the SSD fails, but the hard disc doesn't, you still have your data, and the OS should be able to run completely off the hard disc, with slightly slower performance than the SSD, of course. Like a RAID array in degraded mode. Until you take the machine to an Apple service center to replace the SSD. As opposed to the status quo, where an SSD failure loses your precious data, and renders the machine unbootable. With the SSD backed up to the hard disc, if the SSD fails, you can even choose not to get the SSD replaced, if the machine is out of warranty, instead relying on other forms of backup, like an external hard disc or Dropbox.

Fourth, the macOS filesystem should checksum all files, like ZFS did many years back, to guard against hardware-level corruption. As things stand, Time Machine dutifully backs up corrupt files, which doesn't help. Better to detect and repair the corruption before it's too late, before the corruption propagates to your backups.

These are four ways to improve Time Machine and, more generally, backup on the Mac.

[1] One of many, given Apple's declining quality.

[2] And even then, deleting only as few snapshots as needed to free up the required space. Unlike, say, manually emptying the Mac's trash, which deletes more files than required for the task at hand.

[3] Unchanged pieces of files shouldn't take up space once again. Only the diffs between snapshots should be stored, to reduce space, and so to store more snapshots in the space we do have.

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