How should I go about using an external hard drive for Time Machine and other things?

January 6, 2009 7:34 PM

I have a Macbook and a new external hard drive. I'd like to set up Time Machine, but I don't want to devote my entire new hard drive to back ups. I'm new to this, but I think I want to partition my drive- how do I go about doing that? And how large of a partition do I need for Time Machine?

My Macbook has a 160GB hard drive, of which 84GB are used. The new hard drive is 640GB, so using the entire thing for Time Machine seems like a bit of a waste. I'd like to also use the hard drive to store large video files, which are eating up my laptop's drive at an alarming rate. My questions:

-What is the minimum amount of space I should allot on the new hard drive to Time Machine? My impulse is to divide it in half, which would leave Time Machine 2X my laptop's storage to work with, but I have no idea if this is far too much or far too little.

-I understand OSX has a built in drive formatting utility. Is this the best way to partition my drive? If so, um, how do I actually use it?

A few notes: I am not set on partitioning my drive, but from what I've seen on Apple's site, they intend you to devote an entire hard drive to Time Machine. If you can use a hard drive for Time Machine and also store other stuff on it, well, yay! I just don't want to do my first back up to discover that I'm wrong, and have to start from scratch.

I'm not really looking for other backup programs. I like that Time Machine is easy to use, built in to the OS, and automatic.

Anyone have personal experience with this? My googling and time on Apple's site have not been terribly helpful.

posted by MadamM to computers & internet (13 comments total)

Time Machine will only make an individual file on that drive. I back up my 120GB MacBook drive onto a 500GB drive and several months of backups only account for a fraction of the drive space.
I wouldn't partition it at all, and instead just let Time Machine create it's backup file on the main partition. By Time Machine's nature it won't use up a whole lot more space than is used on the disk it is backing up.
posted by Science! at 7:46 PM on January 6

What Science said.
posted by alms at 7:58 PM on January 6

I was under the impression that Time Machine will keep filling up the drive until it'd full and then start deleting older backups after that. In Applications you'll find Utilities and inside that you'll find Disk Utility. It's pretty self explanitory from there.
posted by bonobothegreat at 7:58 PM on January 6

Sorry, Time Machine will make a single folder on the backup drive to start and each successive backup is really only a backup of changes you made and then references to unchanged files in the original backup and so on. It doesn't create an entirely new backup each time you run the software, it just copies over changed files and notes which files are unchanged.


If you regularly edit large files on your computer, it will fill up the backup drive. If you are a normal user Time Machine will scan your documents folder and note that your "Resume.txt" file has changed, but the entire contents of your "Undergrad Papers" folder has remained unchanged. The resume file will be copied over so the new version is also backed up, but the software will only make a small note that the undergrad folder remains unchanged from the last backup.

No need to partition.
posted by Science! at 7:58 PM on January 6

OK, to clarify, yes Time Machine may eventually use up the entire space available on it's disk/partition. However it's likely that that time is very far away.
posted by Science! at 8:03 PM on January 6

There's no harm in partitioning your hard drive. I myself have split up a 250gb hard drive with 80gb devoted to time machine back ups and the remaining devoted to misc. file storage. When you connect the hard drive, two drives will be mounted. You simply specify time machine to use one of the two partitions. The instructions for doing so are as follows (via Disk Utility):

http://www.kenstone.net/fcp_homepage/partitioning_tiger.html

If your internal hard drive is 160GB, I would make the partition to be used for the time machine backup only 200gb. Retain the rest for storage. Like others have mentioned before me, it will be a long time before time machine starts taking up a lot of space. A 40gb cushion should be more than enough. Then again, if you don't have big files to store on an external hard drive (e.g. movies, etc.), then you may as well split the hard drive in half.
posted by mahoganyslide at 8:17 PM on January 6

what everyone has said sounds right. i would vote for adding a time machine partition. mostly because it is easy to do now and if you do it the other way and are using up the rest of the space at a good pace you will be fighting with your back up for space. if you set the partition you know how much space the backup will take and how much space you have to use as a second hard drive
posted by humanawho at 8:48 PM on January 6

While you're at it, you might also consider adding a 30Gig FAT32 formatted partition in case you want to use the external drive to trade files with a Windows machine in the future.
posted by bonobothegreat at 9:44 PM on January 6

You should do a partition, and half is fine. At the minimum you need to have enough space to back up your entire computer. Any extra space will be used to store multiple versions of files as they change through time, up to the point that space is available. So if you don't give 500+ GB of space, you might not have a complete history going back to the beginning of time, but odds are you'll have it going plenty far back for a reasonable person.

Partitioning is the easiest way to limit how much space Time Machine uses, because it will indeed keep backing up more as time goes on.
posted by kosmonaut at 9:44 PM on January 6

You should chop the disk into "a little bigger than my drive" (so 200GB) and "the rest".

The "rest" partition is for use by Time Machine, the other is for use with Carbon Copy Cloner or SuperDuper to be a bootable clone of your drive.

Drag both drives to "privacy" in the Spotlight system preferences so that spotlight wont index them.

Use GUID partitioning scheme on Intel macs.

For bonus points, you can add a 10GB partition in front of the others that is a clone of the Leopard install DVD. There are many instructions on the net on how to do this.
posted by rr at 10:30 PM on January 6

It´s better to partition your disk. Easily done with Disk Utility.

My setup:

One internal 320 Gb hard disk (Mac Mini)
One external 500 Gb portable drive (LaCie)

Two partitions: 320 Gb and 180 Gb respectively. I use the first to backup and the second one to store data (files, music, movies, etc.)

I don´t use Time Machine (Super Duper is better and faster, but doesn´t work all the time, you have to make manual backups or schedule them to run at certain times) since if the main internal hard drive fails, It would be impossible to boot from the external one (having SuperDuper allows you to do so).

A final word: it´s wise to have redundant backup, this is, another external disk drive to backup your backup drive. Call me paranoid, but I´ve seen many horrible stories of lost data for not being extra careful.
posted by Matrod at 12:04 AM on January 7

The Time Machine partition will have a special icon, so it's nice to keep it separate.

Also, what is your backup plan for the non-Time Machine part of that disk?
posted by smackfu at 6:49 AM on January 7

Use Disk Utility.app to partition your drive. That is found in Applications/Utilities.

Time Machine will keep filling its partition until the partition is full. The nice thing about this is that it keeps old backups in a sane and really neat way. Sometimes you want, not the last version of a file, but one from 3 months ago. If you give Time Machine enough space, you can just scroll back in time and grab that old file and dump it on your present-day Documents folder and start working with it. That's why it's kind of neat to have Time Machine - it's more than just a regular backup. So I'd recommend using as much disk as you can spare.

Also worth knowing is that TM doesn't back up your whole drive, just user-specific portions of it. For instance, the OS is not backed up.
posted by ikkyu2 at 8:58 AM on January 7