4 TB backup drive for 2 Macs

[geokra]

Greetings all,

I've always used time machine to back up my Mac, but recently my wife and I both got new Macs (an iMac for me and a MBP for her). We each have separate backup drives for our computers, but recently I decided to buy an extra 4TB drive to hold duplicate backups. My plan is to keep that drive at work (in case of fire or something else that could wipe out computers and backup drives) and just bring it home once every couple weeks to update the backup.

I set up the drive yesterday but don't remember the formatting I used. I plugged it into my wife's MBP and set up the disk as a new time machine backup drive. At some point in this process I was asked if I wanted to encrypt the backups and thought that sounded like a good idea, so said yes. The actual backup of the computer didn't take too long (a few hours for ~120GB), but the encryption has been running for at least 20 hours and is only about 80% finished. I understand that the encryption will probably take much less time with future incremental backups, but the whole situation has me a bit puzzled about my approach to backups.

Is it a bad idea to be backing up both of these computers to the same 4TB drive? The iMac has at least 500GB of data and could conceivably take days to backup and encrypt on the first pass (although it should be faster due to a much better processor).

My normal backup drive for the iMac has a password for the disk that one must enter to access the drive, but no actual encryption. I assume this is better than no password and no encryption, right? Should I encrypt the backups on that drive as well? I'm not overly concerned about the encryption time on the new drive, but just want to make sure that this makes sense and that it's worth the wait. Am I correct to assume that future backups will be much, much faster?

I think I have a cursory understanding of encryption but just want to make sure I'm being logical. Any tips on drive formatting or anything else involved are very welcome.

Thanks!

 

[geokra]

A quick update. The initial 120 GB backup of the MBP took about 24 hours and then I switched the drive over to the iMac. I started the iMac backup (about 670 GB) a little bit before going to bed and it was finished when I woke up 8 hours later. The backup ran for about an hour before I went to bed, and in that time it had already backed up more than 300 GB (it took ~4 hours to back up 120 GB from the MBP, so about 30 GB/hr), which was about 10x as fast as the MBP.

I'm not sure if it separately encrypted the iMac backup after the backup itself.

 

[Makosuke]

This may be too late to be useful to you, but it's not clear from your description whether you're partitioning the backup drive or not. While it should work either way, I would strongly encourage you to make two partitions on the backup drive (either 50/50, or divided roughly based on the size of the drives on the respective computers). This is what I've done in the past.

Disadvantage of this: If you guess the partitioning wrong, one partition could fill up and start rolling over backups while the other still has lots of free space. Two drives showing up in the Finder.

Advantage of this: If something goes completely haywire with one of your backups (in software, that is), it won't effect the other at all, making it more resistant to disk corruption and such. It will also keep the fairly complicated directory structure of a Time Machine volume from doubling up, since each volume will be independent on disk. You could, for example, erase one partition and leave the other entirely intact, not an option with a single partition.

You should also have the option of formatting each partition as encrypted, putting which I think should bypass the encrypting stage in Time Machine (I would guess based on your description, though could be entirely mistaken, that Time Machine is copying then encrypting, or just encrypting its backed-up data in a disk image, rather than using top-level encryption). Assuming this works with Time Machine, I would expect this to be faster, although I haven't actually tried it so I could be wrong and it's exactly the same.

 

[geokra]

Thanks for the reply!

I had thought about the partitions but have in the past found it to be more of a hassle than anything else. I'll probably go ahead and create two partitions for the reasons you mentioned. I don't mind having to wipe the drive and start from scratch, especially because this is a duplicate backup drive.

Thanks!

 

[ColdCase]

Yeah, for local rotating backups of two Macs I find two smaller drives more reliable and easier to use than one big one. For a TC or a drive on the network its less of an issue because individual sparse bundles are used for each machine.

The type or method of encryption you use shouldn't matter, initial backups are going to be slow regardless