A great deal has changed since Apple introduced Time Machine back in 2007. In those days, I had an 8-core Mac Pro with four 500 GB hard drives spinning at 7200 rpm. The prospect of abandoning expensive conventional backup software such as Retrospect – which coincidentally went off the market for a year just at that time – and running hourly small backups was alluring. And so it remains.
When it came to replace my trusty old Promise Pegasus RAID system, which must have done more than seven years service and worked its way through several sets of hard disks, everyone said go SSD, and I did. Some $/£/€ 1500 later, I am the proud owner of an OWC ThunderBay 4 Thunderbolt 3 RAID enclosure packed with four 2 TB Samsung 860 EVO SSDs. As you’ll have read here, although I still use Time Machine for backups, I’ve had to change my backup policy completely. These articles explain what I now do, how and why.
My original plan had been to use SoftRAID to turn those four SSDs into a single 8 TB HFS+ volume, and carry on running Time Machine just as I have for years. I had several hurdles to cross before I could even turn Time Machine on again. The first was installing SoftRAID, which relies on multiple kernel extensions, which could only be loaded in Catalina by turning off Secure Boot. Not only had that to be disabled in order to install those extensions, but it had to be left off in order to run SoftRAID at all.
Once I’d got a 6 TB HFS+ backup volume (at that stage I only had three SSDs installed), I set Time Machine loose to make its first full backup, of a little more than 1.2 TB. It never returned, having run for several hours at a transfer rate of less than 1 MB/s to drives which were capable of over 1 GB/s, twice the speed of my old Pegasus.
In the end, I was forced to admit that, if I stuck with Time Machine, I’d probably never get another backup to complete. I dropped back to an interim solution of Carbon Copy Cloner while I worked out what to do next.
It was then that it dawned on me that I’d got the whole thing wrong in the first place. What I hadn’t done was looked at what I needed to back up, how often, and to what. I’d simply taken what I’d done for many years and assumed that it is still the best way forward. I needed to rethink and come up with a practical solution which would last as long as those SSDs, say for the next eight or ten years.
Time Machine is an excellent solution for simple problems. My MacBook Pro has Xcode and a suite of Apple apps, and is most-used for development and testing during the beta phase of each major macOS release. For the remaining nine months of the year, it’s a standby and test system, for which Time Machine is simple and comprehensive.
One issue with my iMac Pro is that, like many desktop systems, file usage varies widely. The great majority of the space on its storage is taken up by audio, image and document libraries which change very little over time. Then there’s a small core of files which can change a great deal every day. Many of those are also maintained in the macOS versioning system which is unfortunately kept on the same volume as the document, so hourly backups to separate storage are important to me.
So like many users, I have a great majority of files which need to be backed up infrequently, and a small and active minority which need to be copied to another drive every hour. Although Time Machine handles that transparently, using hard links to directories as well as to files, it’s not necessarily the most efficient way of doing so. It is an excellent way of loading the file system on your backup volume with huge numbers of hard links, which is a challenge that you may wish to spare your backups from.
Another great benefit of Time Machine is its bootable restore feature. If this iMac has to go off for repair, it’s comforting to know that on its return I could just boot from Recovery mode and restore the whole of its internal storage. Or could I? Without loading the SoftRAID extensions my Time Machine backups would surely remain inaccessible from standard Recovery mode, and experience with Catalina is that ending up with a bootable restore is a matter of luck anyway. So what was once a simple solution now looks complex to the point of impossibility.
The most reliable way to restore a full Catalina system seems now to be by installing a fresh copy from Recovery, then restoring or migrating from the contents of your Data volume, something that all good backup software should be able to do.
One by one, the benefits of leaving Time Machine to handle backups with the click of the mouse have been falling away. And until it can store its backups on APFS volumes, Time Machine isn’t going to be ideal for use on SSDs either.
I then made an inventory of exactly what and when I wanted backing up, which runs something like:
- a non-bootable copy of the System volume after each update to macOS, for reference;
- a full copy of my Data volume and its external supplement, updated nightly;
- a full copy of my ~/Documents folder updated hourly;
- a full copy of my main working folder on an external SSD updated hourly;
- a Time Machine backup of that same working folder every hour.
As these are much smaller backups, once the first full backup has been made, and only one of them requires an HFS+ file system on the destination volume, I don’t need to RAID my individual SSDs together at all. That means that each backup drive will be relatively independent, albeit in the same enclosure. This is starting to look more robust and less dependent on third-party software working with changes in macOS.
My next decision was which tools to use for each of these tasks, in addition to Time Machine.