Manage Your Media
For many people, a backup drive may sit on a desk for years, quietly doing its thing without any intervention. For others, two or more drives may be shuttled between locations to provide offsite storage. But in either case, your backup drive won’t last forever. So, in this brief chapter, I look at What to Do When Your Disks Fill Up and explain why you should Consider Long-Term Archive Storage.
What to Do When Your Disks Fill Up
Your bootable duplicates (if any) and versioned backups should continue updating themselves happily for some time. But sooner or later, the drives you use for backups will fill up. (Whether this takes a few months or a few years depends on the rate at which you accumulate new data and the size of your backup disks.) When this happens, you have two options: buy new drives and start over, or recycle. By “recycle” I don’t mean throw your drives in a blue bin; I mean erase them and reuse them for a new set of backups.
One argument for starting fresh is that new drives are virtually always more reliable than old ones. Another is that you can save your old drives as a long-term archive, in case you need to see what you backed up a few years ago (assuming the drive continues to work after all that time). On the other hand, recycling media saves money, not to mention physical storage space. And most people have little need for backups stretching back more than a couple of years.
The choice is entirely yours, but I can give you some tips either way.
If You Recycle Old Backups
For versioned backups, you may want to recycle your drives on a regular basis, before they fill up. By periodically erasing them and starting over with a full backup—instead of relying indefinitely on incremental additions since a single full backup long ago—you reduce the risk of data loss due to file corruption or misbehaving backup software. How often you recycle your media is up to you, but in general I’d suggest recycling mechanical hard drives every one to two years, and SSDs every three to four years.
Do, however, be aware that when you recycle media, you lose all the versioned backups stored since you started that particular cycle. In addition, if you recycle more than one set of media (for example, two or three hard drives), stagger them: do one, wait a week or two, then do the next one, and so on. That way, if you suddenly discover that you’ve erased the media containing an old file you need, you’ll still have a chance to recover it easily from another set of backup media.
For bootable duplicates, as long as there’s enough free space on your destination disk, you can simply erase the disk and start over from scratch. But if you’re running out of space on the disk you use for duplicates, your only option is to erase the disk, use it for something else, and buy a new, larger drive to use for bootable duplicates from now on.
If You Archive Old Backups
When you see that your backup media is close to being full—or when your drive’s warranty has run out and you start losing faith in it—you can set it aside, buy new drives, and start new sets of backups.
Unfortunately, as I discuss just ahead in Consider Long-Term Archive Storage, hard drives and SSDs alike make poor choices for long-term storage (though an older hard drive that you wouldn’t trust for backups may be fine for casual, noncritical uses). In other words, do buy new drives but don’t put too much faith in being able to retrieve backups from your old drives years from now.
If, when it comes time to erase your drives, you still want to maintain a copy of the old data, use your backup software to duplicate your versioned backups and bootable duplicates onto your new (and presumably larger) disks, effectively keeping a single backup lineage intact.
Consider Long-Term Archive Storage
Whether you keep a single backup drive in service for many years or periodically move your data to new drives (see If You Archive Old Backups, ahead), you should give some thought to the longevity of your storage medium. Over a period of years, the data on a hard disk can degrade even if the drive hasn’t been used at all, as the particles on the platters lose their magnetic charge. And SSDs are subject to data loss if they aren’t connected to power at least occasionally (say, once a year).
In fact, all digital media degenerates over time; although the physical process and expected lifespan vary, optical discs (such as CD-ROMs and DVDs), digital tape, and even the flash memory used in SSDs can lose data over a period of years. To be sure, “archival quality” media exists, with claims that it will preserve data for a century or more. (For example, the makers of M-Disc media claim it will last for 1,000 years.) But no one knows for sure, because it hasn’t been around that long yet. And besides, any optical technology you use today might be incompatible with the Macs you have in the future.
As long as you periodically move your active backup data to new media (or restart your backups on fresh media) every few years or so, you shouldn’t have to worry about media degradation. But if you want to keep archives of data that’s no longer on your computer (and no longer being backed up actively)—and especially if you want that data to be readable decades in the future—you should take special care with it. Here are some suggestions:
If you store your archives locally, then whatever media you use for them, store it in a cool, dry, dark place. At least once every five years, copy the archives onto new media.
Alternatively, consider using a cloud service for long-term storage. Cloud services such as Backblaze make redundant copies of your data, monitor data integrity and drive health, and routinely upgrade hardware as necessary. Of course, you’ll pay for this service, but it’s a more reliable way than local storage to ensure that your data continues to be readable for a long time to come. You can save money by using an archival cloud storage service such as Amazon Glacier; see BYOS (Bring Your Own Software) Internet Backups.
Regardless of how you store your archives, verify them (by restoring a few random files) at least once a year.
If you intend for your data to outlive you, make sure your loved ones know where your archives are stored, how to access them, and how to maintain them. For much more on this topic (including what data to preserve for posterity and how to go about it), see my book Take Control of Your Digital Legacy.