Yes, You Can Use One Drive for Time Machine and File Storage

timemachine_iconDuring April, the Rocket Yard focuses on the importance of backups to an overall data security plan. Previously, we discussed how to use the Time Machine app built into OS X to easily and quickly begin backing up data on your Mac, as well as online cloud backup services and their importance to a redundant backup strategy. We also talked about creating bootable backups as a way to get your Mac up and running quickly in the case of a primary drive failure and provided three ways to back up your iOS devices. For the final post this month about the important topic of backups, we’ll take a look at how one drive can be used for both Time Machine backups and for storing your files. First we’ll look at an easy way to do the job, then look at a more complex method that essentially turns your one backup drive into two drives.

The Easy Way
Time Machine saves all of the backups for your Mac in a deceptively innocuous folder on your backup drive named backups.backupdb. That folder contains a folder for each Mac that’s using the drive as a backup drive, so if you’re sharing the drive by connecting it to an Apple AirPort Wi-Fi router, you’ll find multiple folders inside it. For those situations where there’s just one backup drive connected to one Mac, there will be one folder inside backups.backupdb with the name of your Mac on it (i.e., “Bob’s iMac”).

You DO NOT want to put any of your extra file storage into backups.backupdb. Why? Because Time Machine is constantly and voraciously eating space on your backup drive, and it could erase those files if they’re inside backups.backupdb. Instead, you can create a separate folder and give it an original  name like “Files” and put it next to the backups.backupdb folder on your drive (see image below).

TM and Files

Now, if you don’t want to store large files on your Mac’s internal drive, just point to the Files folder on the external drive when you’re saving and they’ll be stored on that big drive. There is a downside to this method; Time Machine files tend to grow to fill the space allotted to them, so eventually your drive may run out of space for those extra files.

MercEliteProWe’ve mentioned before just how inexpensive large capacity hard disk drives are getting. For example, the OWC Mercury Elite Pro in a 6TB configuration with fast USB 3.0 connectivity is just $367.99 as of this publication date. If your Mac has even a 2TB drive built in, you could use all of that spacious drive for Time Machine backups for a long, long time. Or you can consider another idea — using that space for your Time Machine backup and as a place to store all those big video files you’re working on.

The secret word for how to do this is partitioning. Usually, Mac drives come from plants in China, California or Texas with more than one partition or space — the default drive partition and what’s called a Recovery Partition. The latter is what you can use to restore a bad OS X installation by holding down Command+R while rebooting the Mac. The Recovery Partition is hidden from view, even when you use the Disk Utility (found in the Applications > Utilities folder) app to view what’s on the drive. It doesn’t take up a lot of storage, so partitioning a drive into two or more individual drive spaces doesn’t infringe on the Recovery Partition.

There’s an advantage to partitioning the drive into separate Time Machine and file storage partitions — Time Machine will only expand to fill its partition, leaving plenty of space for file storage in the other partition. That 6TB Mercury Elite Pro drive? Split it up into a 4TB partition for Time Machine and a 2TB place for your big files, and you’ve got it made. Let’s do this!

Launch Disk Utility. There are couple of ways you can do this; first is to dig around in your Applications folder until you find the Utilities folder, then double-click that Disk Utility icon. The easy way? Type Command-Space to bring up your Spotlight search window, type in Disk Utility, and then press the Return key (see image below)…


As you can see, this Mac has a Fusion Drive (part SSD, part HDD) installed. It also has an external 2TB drive named RAID 1 Media. For both the Internal and External drives, the physical disk name (Fusion Drive, RAID 1 Media) is different from the volume name (Macintosh HD, RAID1). To add our partition, we want to click on the external drive physical disk name — RAID 1 Media. The next step? Click on the Partition button in the Disk Utility toolbar. The following dialog appears:


To add a second partition for data storage, click on the + icon below the circle that represents the total storage available on the drive. Now sadly, this test drive doesn’t have a lot of space available, so we’ll just make a 150GB (.15TB) partition to put files into. To size the drive to the proper capacity, either move the dot around the circumference of the circle until you see the desired capacity in the “Size” field, or type the capacity into that field. Be sure to give the Partition a name — in this example, “My Stuff” — and choose the format, which should usually remain OS X Extended (Journaled).

Now click Apply. Disk Utility verifies the disk and the file system, checks the existing Journaled HFS Plus volume, and then checks the catalog file. This step can take a while if you already have a Time Machine backup on the drive, as there are a huge number of files that are checked. Once the partitioning is complete, Time Machine will continue to back up to the original volume since its name has not been changed.

The process of creating a partitioned Time Machine/data drive can also be done when you’re setting up a new drive, and will take a lot less time. Just note that you’ll need to give each partition a name (perhaps “Time Machine” and “Data”), then use the Time Machine System Preference to select the Time Machine partition.

One final comment — now that you’re storing some data on an external drive, you’ll need to back that new data up as well. This is a case where a redundant backup strategy can help, as that data could theoretically find a backup home on another drive or in a cloud backup system.

Keep your data secure
We’ll continue to implore you to do your best in terms of backing up your Mac and iOS devices, even as we get out of Backup Month and into the rest of the year. Now that you know that you can use one big drive or array as both a Time Machine backup drive and as a place to store even more data, what are you waiting for? Take a look at all of the external storage OWC has to offer, and make an investment in the security of your data.


  • Sorry but I disagree with this advice. With disk storage inexpensive this is not the ideal way to protect yourself. Drives fail. That’s why we backup. If the combined time machine and documents drive fails you will have lost your documents and your back up. A more sensible approach is to have a dedicated time machine disk and a dedicated bootable clone. Only if you are running out of space for documents and only if you are disciplined about a second way to back up would I go this route

    • Thanks, Alan, you just saved me from writing the same response. When I first read the beginning, I couldn’t believe he was going to do this. So, if I move files to a drive containing my TM, even as discrete partitions, I won’t loose everything? The problem with TM, as the original author confesses is how much space it will consume. Since it’s one TM scheme per Mac at a time, all TM data must fit in one partition. And to be secure, you really need to have a second TM disk which takes up the same amount as the first. I now use 2 separate 6TB external disks to back up my data and they are both nearly full.

    • So why have time machine at all and just back up to Carbonite or another web service that will mail you a hard drive if you have a failure?

      • The answer is “redundancy”. Never rely on a single backup, whether locally to an external drive or remotely to a service like Carbonite or Backblaze. If your primary backup is down (your local drive is toasted in a house fire), you still have the remote backup. A global catastrophe takes out the Internet and Carbonite, you still have the local drive. If both bite the dust, things are probably bad enough that you won’t be worrying about your data…