2/21/23
9:00 am

Why You Should Never Partition Your Backup Drive

It is tempting to partition a backup drive so you can use some of that storage space for other things. But you should avoid doing so for two key reasons.

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Video Transcript: Hi, this is Gary with MacMost.com. Let me tell you why it's a bad idea to partition your Backup Drive. 
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So I often see Mac users get an external drive for a backup and then decide to partition it and use part of that drive for something else. For instance, let's say you start off with a new Mac Mini. It could be an iMac, Mac Studio, MacBook Pro, MacBook Air. Whatever. You've got a new Mac and let's say it has a 1TB internal Drive. You do the smart thing and decide to start a backup. So you buy an external drive. You get a 4TB external drive. They are not that expensive now a days. You can get one for about $90. It just plugs right in. It doesn't require any external power and it is so small you barely notice it on your desk. So then you're ready to backup. But then you realize you only have 1TB in your internal drive and not all of that is even used. A 4TB drive seems excessive to back everything up. Maybe you should do something else with the rest of that space. 
So you decide, maybe, to partition it. Create a 2TB backup partition and a 2TB partition that you can use for something else. For archiving old projects and such. Then you set it up so that the backup is just backing up to that first partition and the second partition is free for you to use for whatever you like. That sounds like a pretty good deal except there are two main problems with it. The first one is a show stopper!
So let's say you have a file on that Other Stuff partition. Let's call it File A. It's an important file. Let's say one day that hard drive fails on you. Hard drives fail. They can fail for a variety of reasons. It may not be that the hard drive breaks. Maybe you drop it. Maybe it gets crushed. Maybe it melts in a fire. Maybe you loose it or it gets stolen. A lot of reasons that that drive can suddenly not be available to you anymore. When that happens that file is gone. It was on that other partition. You weren't backing it up anywhere. But then you say, well wait a minute. I'm backing up.  Can't I backup external  drives as well as internal ones. I'll backup both my internal drive and anything that is on that Other Stuff partition to the backup partition. Maybe I'll even make the backup partition bigger or maybe I don't really need to. So I am backing up my other stuff. So now I have two copies of that file. One in the partition where I access it and the other is a backup. This will actually help in some situations. If you accidentally delete that file from Other Stuff then you can recover it from the backup partition. Or if you make a change to it you can go to the backup partition in Time Machine and recover an older version of it. So it will help in some situations. 
But you know what situation it doesn't help with is if again you loose access to that drive for whatever reason. Now you've lost both your backup and all the things in Other Stuff even though you actually had two copies of that file, an original and a backup. Both of those are now gone because you don't have that drive available  anymore. The short term for this is basically Single Point of Failure. Your original and your backup are on one drive. That drive acts as a Single Point of Failure if you loose the drive, if it gets stolen, it melts, if a meteor hits it, whatever, you have lost the original and the backup in one single failure. For this reason alone you should never partition a backup drive. Just have it as your backup. Don't have any other files stored on it anywhere in another partition or otherwise.
Now here's another reason this is a bad idea. You may think that because you just have  1TB of internal storage and maybe half of that is being used that 2TB is more than enough space to back things up. Indeed, it will work fine for a little while. But eventually all of the space in your backup will fill up. Now how is it possible, say if you have ½ a TB of data that it could fill up a 2TB drive. Remember, Time Machine is an incremental backup. So it is going to keep versions of your files as you change things. Like, for instance, as you write your novel and your word processing document changes everyday it's going to save new versions of that to the backup. So you can go back in time to yesterday's copy or last month's copy or the original copy from last year. In addition, if you delete files it is still going to save a copy in the backup. So you create a large file, maybe a video project, and now you delete it. The last copy of that file is still going to be saved in your backup. That's the whole point of a backup. Because if it was an accidental deletion then you want to be able to recover it and you may not realize that you accidentally deleted it until a few days, a month, six months later. So the backup drive will slowly fill up as you create files, modify files, and delete files. So even if you're not using anywhere near 2TB of storage right now you eventually will hit the limit on the drive. 
Now ideally it would take years to do that. But it is going to happen a lot sooner if you decide to partition the drive and only have a 2TB backup rather than having a 4TB backup. So you want to give Time Machine as much space as you can. Don't do something that's going to limit the amount of space it has to backup your files. If you really need an external storage a better situation is to just get another drive. This eliminates both problems. So you have your 4TB Time Machine drive. It costs about $90 now. Maybe get another drive. A 2TB or a 4TB drive. The 2TB drives are now about $60. Or just dedicate that 4TB drive to your backup and hopefully your internal drive is enough for all your file storage. If not, you could always use Cloud storage like iCloud Drive or any other cloud service to expand that. 
So I hope this makes it clear why you should avoid partitioning your Time Machine backup drive. Give Time Machine as much space as you can and avoid a Single Point of Failure. Thanks for watching.

Comments: 17 Responses to “Why You Should Never Partition Your Backup Drive”

Bent, Denmark

2 years ago

Thank you for another instructive video.

I have a 50 GB iCloud storage and have chosen not to include Photos App in my iCloud storage. It will fill up all storage. (I am aware that photos are not synced between devices).

First I wonder if the Time Machine back up to an external drive does include photos in the Photos App.

Secondly I wonder what is the best procedure to back up Photos App-photos to a separate external drive. Making a full backup each time seems to be too much.

Gary Rosenzweig

2 years ago

Denmark: Yes, Time Machine backs up all of your files. Since your Photos library is a file (a library package) in your Pictures folder, it will back that up too. You can just look and see. If you want to back up to another drive, just drag and drop that Photos Library file to that other drive to make a copy of it there.

Bent, Denmark

2 years ago

Thanks Gary.
Have you considered making a video on how to backup and restore photos placed in the Photo App using the Time Machine

Unlike other files in the external backup made by the Time Machine, individual items within the photo library can not be seen. Apparently the full photo library must be restored. Will such a restore overwrite the existing MAC photo library with the same name or where will it be placed in my MAC file structure?

Gary Rosenzweig

2 years ago

Denmark: Hopefully, if you accidentally delete a photo and need to get it back you can find it in the Recently Deleted album. If you can't, then you can restore the photos library, but don't have it replace the current library, just appear as a new library in your Picture folder. Then open that library up, find the photo, export it, switch back to your current library, and then import it. Then you can delete the restored old library.
Or, if you are careful and willing to explore, you can look directly on the Time Machine drive, find the library there, use Show Package Contents to go inside, find the image (difficult) and then copy it and paste it on to your regular drive for importing. Just be careful not to move or change anything in the Time Machine drive, just look and copy.

Frank Scully

2 years ago

If Denmark does not include Photos App in iCloud storage, then his photos taken say on an Iphone would not be on his Mac unless he manually copied them there. Hence his backup would not be complete

Donald Cope

2 years ago

After doing a bit more research, I found the following in Apple Support: "Apple File System (APFS) allocates disk space on demand. When a single APFS container (partition) has multiple volumes, the container’s free space is shared and can be allocated to any of the individual volumes as needed." I must have created two volumes in one container (partition). Therefore, my Time Machine (one volume) can use all of the space (4 TB) if I do not use the other volume. Is this reasonable?

Gary Rosenzweig

2 years ago

Donald: It is reasonable, but I would still avoid it. No reason for that other volume since you shouldn't use it for anything. But I suppose it may not be worth messing with if you already have it set up and just remember not to use it.

Bent, Denmark

2 years ago

Thank you Gary for 3 very good suggestions (recently deleted, restore etc., looking into the Backup library (with care)). And Frank thank you for your “warning”. I am aware of the non-sync situation.

Steve C.

2 years ago

I have a very specific for having 2 partitions (APFS) on my backup drive, which happens to be an external SSD.

- Partition 1 is for Time Machine backups.
- Partition 2 is for ad hoc file and folder backups, e.g. key snapshots and external data from remote development.

I do not store any original content in Partition 2. It's all copies. If I lose the drive I only lose backups.

Am I mis-thinking this?

Gary Rosenzweig

2 years ago

Steve: Not sure where the files for partition 2 are coming from. From other external drives? If so, just include those external drives in your Time Machine backup. From servers? If so, then why not download the "backups" of those to your main drive, and then let Time Machine back those up as normal. Then you have a history for those files.

Steve C.

2 years ago

Hi Gary,

It's mostly a matter of convenience. I can organize ad hoc backups with named folders to make it easier to find things, compared to the TM app. Some of the files are also backed up in TM, and even iCloud. But I've found the organized key snapshots to be a useful adjunct to TM.

I save known-good source code, so I don't have to remember TM date/time. I also backup cloud dev servers.

I've had TM volumes get corrupted. Don't know if APFS volumes can corrupt each other though?

Gary Rosenzweig

2 years ago

Steve: I don't know if one volume can "corrupt" another. Probably rarely if ever. More likely that the whole drive goes.

Steve C.

2 years ago

Gary: My instinct too. In any case that second partition only has replaceable and temporary files, e.g. for transport to another machine. The TM volumes that got corrupted were probably spinning disks, not SSDs. I do think the large quantity of filesystem objects on a TM volume does make it more subject to "cosmic rays" and other random damage. Cheers.

Gary Rosenzweig

2 years ago

Steve: Cosmic rays, no. But power spikes, static electricity, accidentally pulling the cable out in the middle of a write, and just drive parts failure is what you need to worry about.

2 years ago

I can't seem to find it at the moment but I thought with Time Machine you had the option to have it delete backups if there was not enough space to hold the next backup?

As an alternative to a NAS you can get something like a Western Digital My Book Duo which has two hard drives that can be setup in RAID so if one drive fails the other should have an exact copy. Then you just replace the bad drive with a new drive (has to be the same size disk) and all the data should move to the new drive

George

2 years ago

I like the advice. I have not followed it. But I think not following it makes things very complicated. So I plan to avoid single points of failure by using backup on one partition on one drive once I get more drives.
One thing I like is having two copies of all original data: A and B.
I want to put one set ‘A’ in a safe or safety deposit box, and monthly swap things with ‘B’ so that one is always somewhere else.
But with COVID, the split was hard to do.

Now I can do that split.

Tim

2 years ago

Reason one, of having the drive "split" and running out of space on one partition and needing it on the other is not an issue if using APFS partitions. Given the ability to add a second "Volume" to an APFS partition allows me to have the entire drive available for Time Machine, while still giving me a location to put some large temporary / transient files.

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Why You Should Never Partition Your Backup Drive

Comments: 17 Responses to “Why You Should Never Partition Your Backup Drive”

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