Does the Time Machine backup drive have to have at least the same capacity as the boot drive?

[hajime]

Hi, supposing that I get a base Mini M4 with 256GB SSD and a 4TB external drive. Then install and boot MacOS from the external drive. Do I need to have an external backup drive of 4+ TB to use Time Machine properly?

 

[theluggage]

Time Machine keeps multiple versions of old files so your TM drive needs to be larger - maybe at least twice the size - than the amount of data you want to back up.

I guess a smaller TM drive will work initially when you’ve only actually used a fraction of your 4TB boot drive, but, at the risk of stating the obvious, if you need a 4TB boot drive then, eventually, you’ll need a 4TB+ drive to back it all up.

 

[HobeSoundDarryl]

General rule of thumb for ideal TM is add up ALL of the capacity you’ll want backed up by TM and then multiply by at least 3. “All” includes adding in external storage if you want anything stored on it backed up too… as well as any other Macs in the home you also want backed up.

If it’s just 1 Mac with only the 4TB of storage, 4 X 3 = at least 12TB (ideal TM drive size).

Why so much more? It’s in the name. There are TWO big benefits to TM:

1. A dead simple backup system that can run itself and
2. The ability to step back in time to recover from many versions of files

If it was only #1, you could get by just fine with only a little more storage than what you store now. If that was-say- 500GB of actual data on the combo of 4TB + 256GB, you’d need slightly more than 500GB (for now).

But #2 is where the real magic lies. The more TM space you have, the further back in time you can go. If you accidentally delete some important files but don’t notice for a few months, a big fat TM storage pool will likely let you travel back through those months to retrieve them. A pool so tiny it is barely bigger than actual data stored offers no time travel. Those files would be lost.

With TM, GO BIG! if yiu truly want just a clone of current storage in the least possible space, consider the free Carbon Copy Cloner or SuperDuper options. But again, note the name: it’s called Time Machine NOT Apple Cloner for a very important and valuable reason.

TIP: since you are onto the value of backups before the crisis that usually triggers interest, a very good idea is get at least TWO TM drives… one in active use with Mac… plus one recently in active use but stored safely offsite. Rotate the two regularly. Why? Very real fire-flood-theft scenarios will typically take out BOTH the Mac and the TM drive sitting right next to it. One recently fresh backup stored offsite offers almost complete recovery.

Big storage is towards dirt cheap. Go BIG here for data peace of mind. Should the data crisis ever hit, you’ll be so glad you spent relative peanuts today for easy recovery. And should it be less than a full crisis such as discovering you deleted some important files weeks or months ago or key work in progress creations got corrupted in the last few weeks or months, the ability to step back and recover is a great benefit.

 

[kschendel]

It has to be at least a couple times larger than the amount of space in use on your drive.

You really want it to be larger, though, several times larger than the space that you expect to have in use.

 

[hajime]

General rule of thumb for ideal TM is add up ALL of the capacity you’ll want backed up by TM and then multiply by at least 3. “All” includes adding in external storage if you want anything stored on it backed up too… as well as any other Macs in the home you also want backed up.

If it’s just 1 Mac with only the 4TB of storage, 4 X 3 = at least 12TB (ideal TM drive size).

Why so much more? It’s in the name. There are TWO big benefits to TM:

1. A dead simple backup system that can run itself and
2. The ability to step back in time to recover from many versions of files

If it was only #1, you could get by just fine with only a little more storage than what you store now. If that was-say- 500GB of actual data on the combo of 4TB + 256GB, you’d need slightly more than 500GB (for now).

But #2 is where the real magic lies. The more TM space you have, the further back in time you can go. If you accidentally delete some important files but don’t notice for a few months, a big fat TM storage pool will likely let you travel back through those months to retrieve them. A pool so tiny it is barely bigger than actual data stored offers no time travel. Those files would be lost.

With TM, GO BIG! if yiu truly want just a clone of current storage in the least possible space, consider the free Carbon Copy Cloner or SuperDuper options. But again, note the name: it’s called Time Machine NOT Apple Cloner for a very important and valuable reason.

TIP: since you are onto the value of backups before the crisis that usually triggers interest, a very good idea is get at least TWO TM drives… one in active use with Mac… plus one recently in active use but stored safely offsite. Rotate the two regularly. Why? Very real fire-flood-theft scenarios will typically take out BOTH the Mac and the TM drive sitting right next to it. One recently fresh backup stored offsite offers almost complete recovery.

Big storage is towards dirt cheap. Go BIG here for data peace of mind. Should the data crisis ever hit, you’ll be so glad you spent relative peanuts today for easy recovery. And should it be less than a full crisis such as discovering you deleted some important files weeks or months ago or key work in progress creations got corrupted in the last few weeks or months, the ability to step back and recover is a great benefit.

Thanks for the detailed analysis.