How to use multiple hard drives with Time Machine

By | May 3rd, 2016

Time Machine
Apple’s Time Machine software helps you create a backup of your Mac hard drive. What if something happens to the external drive you’re using for the Time Machine backup? If you’re following our 3-2-1 Backup Strategy then you’ll be protected, but you can do more, too. How about using multiple backup drives with Time Machine? Here’s how.

Some background on Time Machine

Time Machine is more than just backup software for your Mac. It’s also an archival tool. It keeps moments in time for you to look back on, so you can recover deleted or missing files or even revert to older versions of files you’ve worked on.

Get more details about Time Machine in our guide How to back up your Mac.

Time Machine stores hourly backups for 24 hours, daily backups for the past month, and weekly backups for all previous months for as much space as you have on your Time Machine backup drive. The oldest backups get deleted when the drive fills up.

You can use a single Time Machine backup drive with multiple Macs. You can also use your Mac with more than one Time Machine backup drive.

Disk rotation

This technique is borrowed from corporate IT professionals: Disk rotation. The old adage “Don’t put all your eggs in one basket” is the reason. While Time Machine is great backup software, it’s not foolproof. If your Time Machine backup drive dies – as hard drives do – all of that data will be gone.

Interested in hard drive failure rates? So are we! You see, we use over 60,000 hard drives! Read our Hard Drive Reliability Stats to learn more.

Having Backblaze is a great way to fix that, of course, because your data is also backed up to the cloud. They’re complementary to one another: Backblaze tracks the last 30 days of changes to your files, for example, while Time Machine will keep track of as many changes as it can within the storage capacity of your backup drive. So it’s nice – ideal, really – to have both.

Fortunately, Time Machine handles disk rotation with aplomb. You can attach a second hard drive and use it with Time Machine with only a couple of clicks. When Time Machine is connected to your first backup drive, it will back everything up. Then it’ll do the same for the second one. Time Machine backs up everything that’s changed on your Mac’s hard drive since the last time that backup drive was connected. So each drive will keep a complete Time Machine archive.

Here are step by step instructions:

To use multiple drives with Time Machine

  1. Connect your second hard drive to your Mac.
  2. Click on the Time Machine icon in the menu bar, then click on Open Time Machine preferences.
  3. Click Select Disk.
  4. Select the drive you want to rotate, then click Use Disk.
  5. Time Machine will ask you if you want to replace your existing Time Machine drive, or use both drives. Click Use Both.

Time Machine will now back up to each individual drive as they’re connected.

When you want to check on your Time Machine backups later, all you need to do is hold down the option key when clicking on the Time Machine icon in your menu bar. You’ll see Browse Other Backup Disks. You can use that to browse whichever Time Machine archive you’d like.

The same process works if you mix a Time Machine backup drive with Apple’s Time Capsule network device (a home Wi-Fi router with built in backup drive). You can back up to both without any problem.

Using this procedure, your data is backed up on two (or more) drives. You can leave one at home and leave the other in the office, for example. That way you’ll never be without a backup you can recover from quickly and easily.

Have you set up a disk rotation scheme with Time Machine? Or do you still have questions? Let us know in the comments.

Peter Cohen
Peter will never give you up, never let you down, never run around or desert you. He also manages the Backblaze blog.

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Category:  Backing Up · Mac Love
  • Ctv Photog

    Can I back up my computer hard drive and an external hard drive at the same time?

  • Z Ixazaluoh

    hi, thanks so much for your article!

    On disk rotation with Time Machine, can you be backing up both external disks simultaneously, so you can simply plug them in and forget about it? And they will record the exact copies?

    Or, do you have to choose just one at a time, and manually switch them via Select Disk?

    (Since you said,
    “Time Machine will now back up to each individual drive as they’re connected.”, i wish to make sure i understand correctly, if you mean “as they’re connected” is to have both disks plugged in to the mac, and “use both” selected…

    if you mean it is to to have both disks plugged in to the mac,
    but can “select disk” for one or the other only at a time.)

    Thanks for clarifying for me! :)

  • Mr Hanky

    Can I use Backblaze for my 4 internal HD on my Mac?

    • Yes, and external drives as well if they’re not network-attached.

  • Anyone know if its possible to select what to back up on TM? I have two external drives attached as TM backup, but one of them is smaller capacity and is full. I would like to tell TM to backup selectively on *one* drive, and the other as is. Thanks for the help.

    • Timothy Shoultz

      Go to Options in the TM preferences and you can choose what items to exclude from the backup. Hope that helps

  • Is there any way to sync two hard drives that I’ve used with time machine so that they both have each other’s content, or better yet, the bigger one has all the data/backups on it?!

    I currently have two hard drives, but they contain different backups afaik..

  • Hein van Dijk

    Hi Peter,

    I’m using disk rotation and it works fine. Yet I have a problem: both of my time machine disks still do backups of an old external raid 0 disk that doesn’t exist any more. These backups fill up my time machine disks of course. How to get rid of these particular backups. When I entered Time Machine, I tried the command: “delete all backups of……”, but nothing happens.
    Can you help me?

  • Stefano Giovannini

    Can you use different options when you use 2 Time machine drives? I would like one 4TB drive to backup my imac and 4 small portable SSD drives, but use a smaller 2 TB drive to backup the iMac only and the most recent SSD with the recent LR catalog and photos

  • RobNash

    You star, thank you for this information!

  • Theresa M Callahan

    Hello there: I had a problem with my IMAC and had to reformat the drive and reinstall the operating system, I did this with the assistance of Apple and they advised me at the time that I would be able to access my data within the time machine backup files. They said that I did not have to restore the files.. that I could keep them on the external hard drive and continue to use them. I am finding out now that I am unable to copy and or move the backed up data – I can not seem to access it at all. How do I get to the files that are within the Time Machine backup file that is stored on an external drive? I can not restore the data to my IMAC, there is too much data for my IMAC hard drive to hold. I need to work with these files and instead of just copying them over to an external hard drive, I took the advice from Apple and thought I could use this data within the backups. The backup file within the Time Machine backup does not allow file level access. Can not rename, copy, or move anything. HELP! Really, Help. Now how do I access and work with the data within the backups? Thanks.

    • Darren O’Brien

      When you open time machine hit Shift+CMD+C and it might show the older backups from the old computer (this worked for me). Or you could log in as a Root user (google how to do this), browse the backups in Finder and change the permissions.

      • AmericanWoman

        I have been able to sort through all of the backups and all the files I need are there- but the time machine backup does not allow file level access. It’s saying that in order to get access to these individual files I must restore them to my mac. Can I do a partial restore and only transfer over the files that I need? I’m afraid to go into the root, I could really screw thjngs up.

        • Darren O’Brien

          Are you accessing the files through Finder or through Time Machine?

  • George Singer

    I would like to see Time machine spanning disks ( to avoid having time machine delete old backups )

    • Scott Beeker

      If you use a NASD drive like say a Drobo you can do this. So my Drobo has 5 bays which is 1 redundant drive for 4 hot. (RAID) When you create a file share you make it TimeCapsule accessible. Allocate a virtual size. They recommend 2-3 times the size of your drive but you can use the entire Drobo. My Drobo has 5 4TB drives. I also have 4 more external drives that are not RAID on it. I do three backups. 1 to the Time Capsule device, one to the the Drobo which is in RAID configuration , and a third to a USB drive hooked to Drobo which is exact size of my computer drive. I travel so I always grab the USB drive. While on the road my Drobo is remotely accessible for backups as is the USB drive.

      The Drobo also has more capabilities like web pages, mail, mysql, photo serving, flex etc. Also copies all my favorite TV shows from my PVR so I can view remote.

      But my key point is you just need a NASD RAID drive that knows how to serve TimeCapsule. Drobo is 1 of these. I use a DRobo5N

      FYI when you go to restore you have to hold the option key down when accessing the multiple Time Capsules.

      FYI the Drobo is also used to back up all my iPad, phones etc. It has a locality app that when I go home my devices automatically backup.

      • George Singer

        My intention is to use two or more drives in a sequential manner, not using RAID, a rather expensive proposition. My present Time Machine uses a 6TB drive, and TM purges the old files rather frequently. I am not interested in duplicating the backups, just to enlarge the TM repository without spending a ton of money in RAIDs.

        • James Bond

          RAIDs are not expensive.

          A simple RAID 0 box is under $50. Drop two 6TB drives in for a single 12TB volume. You could even use your current 6 TB drive if its a bare drive.

  • How do I migrate Time Machine backups split over two drives, to one larger drive?

    • I’ve found the answer to that myself. Do a Time Machine back-up. Immediately after, do another Time Machine back-up. These will go to both disks one after the other. Then choose the disk with the earliest back-up (not of the latest two back-ups but the oldest of all) and that is the one to migrate over via Finder (Shift-Option-Command-V), Disk Tools, SuperDuper, whatever.

  • Sydney Tsai

    For HDD alternative, I prefer using SSHD 3.5,(Hybrid of small SSD with HDD) they cost a bit more than traditional HDD, but they perform better on random access, where Time Machine does on it’s version backups.

  • photon

    This is something I’ve been doing for the last year or so and highly recommend. I’d like to see a separate discussion about using a Time Machine drive to store other data. I know there are recommendations to only do this using partitioning but I’ve never seen an in-depth discussion of the pros and cons/ limitations of shared use of the drive vs. partitioning. Also, I’d love to see a discussion about using the same drive for TM backups for multiple computers, again with and without partitioning. Thank you.

  • joshuatj

    Sometimes I envy Mac users. Is there something as robust as Time Machine for Windows users?

  • Bob Bellenghi

    You said: “Backblaze tracks the last 30 days of changes to your files, for example, while Time Machine will keep track of as many changes as it can” How do i access the various versions and days of my previous 30 days?

  • innerspacerobot

    I use 3 disks in Time Machine for local backups:

    – A local spinning USB powered disk that is always attached. This is the fastest way to get back accidental deletions. This doesn’t have many backups due to size.
    – A time capsule at the other end of the house that is more physically isolated. Being a LAN/NAS device this is slower, but provides some isolation if fire were to take out a lot of the house. This is always connected.
    – Another larger mains powered disk that I only connect for a few hours every week or so – when Time Machine nags me. This is the longer term back to guard against infections, something wiping all accessible / connected disks, etc.

    • Excellent strategy!

      • MrSizzle


        If I would like to use a strategy of cascading drives, attached to my Time Machine, for continuous backup, is that possible? Let me explain:

        I have a 1GB Time Machine (fairly old). It is full of backups and no extra space. Can I plug a 2nd drive into the TM and have it ‘cascade’ to that drive for backups? And then a 2nd attached drive, that is ‘cascaded’ to next? Then when all full, it eliminates old backups and starts at the Time Machine again. Does that make sense? Thx.