PDA

View Full Version : Time Machine backing up to a USB Flash drive?




RedTomato
Sep 14, 2008, 09:25 AM
Hello,

I just saw 16GB USB flash drives on sale for 25, which isn't much. That makes me wonder if it's becoming feasible to use Time Machine to back up to a USB flash drive?

Obviously you can't back up the whole system, but 16 GB would be enough to cover the documents folder of a lot of people. 64GB flash drives are out now, and that's nearly enough for a whole Macbook Air.

An advantage is it would use less battery power than backing up to a 2.5'' portable drive.

One issue is wearing out the write cycles of the flash drive, but they are so sturdy nowadays, and also TM doesn't cycle memory that much - only writing new stuff each hour (while plugged in) and erasing old stuff when the drive is full.

Interesting? Do people already do this? A google search found nothing.



DMC-12
Sep 14, 2008, 02:16 PM
Doesn't the TM backup drive have to be at least the size of your Mac's hard drive?

Eidorian
Sep 14, 2008, 02:18 PM
It'll work just fine. Just exclude what you don't want backed up to the flash drive to save on space.

kurzz
Sep 14, 2008, 11:23 PM
Doesn't the TM backup drive have to be at least the size of your Mac's hard drive?

Not unless your hard drive is entirely filled up. Time Machine only backs up what you currently have on the HD..it doesn't backup the empty space!

DMC-12
Sep 15, 2008, 12:27 AM
Not unless your hard drive is entirely filled up. Time Machine only backs up what you currently have on the HD..it doesn't backup the empty space!

OK, this makes sense. Good to know.

Shagrat
Sep 15, 2008, 03:06 AM
Sounds like a cool idea! Good thinking. Will try it out myself!

RedTomato
Sep 15, 2008, 05:57 AM
It's a shame you can't set TM options on a disk by disk basis - I'd like to set up something like this:

- working documents folders backed up via TM to a 16GB USB stick while I'm out or travelling.

- At home or the office, have TM back up the entire HD to my 1TB Time Capsules.

kurzz
Sep 15, 2008, 11:14 PM
Also keep in mind, however, that Time Machine keeps multiple copies of your backup, hourly, daily, weekly, monthly, etc. So, the larger the space available to it, the "further back in time" you can go.

simonsimon
Oct 7, 2008, 01:22 AM
I've been trying to get Time Machine to back up just one folder to a 4GB usb flash drive.

I've excluded everything except for this folder (at the top level on my hard disk) including invisible files and folders. There's only about 500mb of stuff in the folder.
However, when it tries to do the backup I get a message saying that there's not enough space, that it needs 10gb. I tried again with just an excel document (24kb) in the folder, same problem! When I do (exactly) this to an external hard disk with 12gb free, no worries, it backs up, and the backup folder on the hard disk only takes up 88kb.

Does anyone know how to make this work? Why does Time Machine want such a huge amount of free space for a small folder? Even with the 500mb folder it wants 20x the space.

RedTomato
Oct 7, 2008, 03:16 AM
I've been doing some poking around, and I suspect having that folder at the top level might make a difference. Try backing up a single folder on your desktop or just your documents folder, or a single folder in your home, and see if that makes a difference.

rouquin
Oct 7, 2008, 05:46 PM
Actually, this is probably a case of you could, but should'nt.

USB memory sticks have a limited number of read and write operations before they fail, whilst this is not a problem for moving data around, or carrying it with you, it does become an issue if there are lots of updates occurring, i.e. something like time machine accessing the stick every hour and doing lots of read and write operations.

It might be fine for several months (we are talking 10's of thousands of reads / writes after all), but I would not want to trust one as being my only backup.

Littleodie914
Oct 7, 2008, 06:20 PM
It should work, as many other posters have mentioned, but one thing I thought I would add is the serious speed difference between a flash drive and an external HD. Flash drives are much slower, both for reading and writing, than traditional "platter" drives.

Flash storage is getting faster, but you'll still see huge differences (close to 10x faster on a traditional drive). :eek:

RedTomato
Oct 7, 2008, 06:34 PM
Actually, this is probably a case of you could, but should'nt.

USB memory sticks have a limited number of read and write operations before they fail, whilst this is not a problem for moving data around, or carrying it with you, it does become an issue if there are lots of updates occurring, i.e. something like time machine accessing the stick every hour and doing lots of read and write operations.

It might be fine for several months (we are talking 10's of thousands of reads / writes after all), but I would not want to trust one as being my only backup.

Bzzzz. Completely wrong. Time Machine doesn't do lots of reads and writes on a USB stick or the backup drive. It only writes what's new since the last backup. Which is usually not much.

And while I'm not completely clear how it knows what to back up, I think it works with the OS to maintain a list of what files have been touched, then when a back-up is done, that list (which is possibly stored on the host drive) is cleared.

There are a couple of other ways it might know what needs to be backed up, but none of them involve having to scan through every file on the USB stick / backup drive.

rouquin
Oct 7, 2008, 07:19 PM
Bzzzz. Completely wrong. Time Machine doesn't do lots of reads and writes on a USB stick or the backup drive. It only writes what's new since the last backup. Which is usually not much.

And while I'm not completely clear how it knows what to back up, I think it works with the OS to maintain a list of what files have been touched, then when a back-up is done, that list (which is possibly stored on the host drive) is cleared.

There are a couple of other ways it might know what needs to be backed up, but none of them involve having to scan through every file on the USB stick / backup drive.

I'm sure that your right and time machine is very clever in keeping track of the changes and minimising the backup device access.

Nonetheless, I would not trust a USB stick as a long term backup device. I tend to change files throughout the day as I work, so the work that time machine does it very real. Even if there have been no changes, time machine will still access the backup device and write some information (use the backup now feature a couple of times when nothing else is going on and no files have been changed and watch the activity monitor). Those reads and writes soon clock up over a few months.

Please note that I am using phrases like 'long term' and 'months', duty cycles that do not trouble most hard disks too much (yeah I know there are always going to be some duff ones).

Would you trust a USB stick with your time machine backup?

simonsimon
Oct 7, 2008, 11:46 PM
I have an external hard disk at home that I back up my macbook to every time I go home (every few days), and I need the USB backup for those in between times. So system, music, photos, all the big stuff is all backed up there. I just need two or three days of work backed up for the in-between.

If it only lasts a 6 months, that doesn't matter. It's better than carrying around a hard disk.

Interestingly when I choose a folder on one of my smaller external disks (only 120gb, my internal is 320gb) then it says I only need 5gb free. Not 10gb.

Does time machine decide how big the disk needs to be based on your hard drive capacity, rather than actual size of data you want to back up?