View Full Version : OT: Time Machine & USB disks

2011-07-25, 06:27
Sorry for the off-topic post, but I know there are quite a few Mac users around here and am hoping one of you might know the answer to this.

My daughter has a Macbook and needs an inexpensive external disk for use as a Time Machine backup device. I bought her a bog-standard 320GB Freecom USB2.0 bus-powered 2.5" disk. It seemed to work fine for several months, then Time Machine said it had failed. So I reinitialised it using Windows diskpart and all seemed well again. Then a month or so later Time Machine said it had failed once more. OK, perhaps the disk is just faulty - except that after I reinitialise, it seems to work perfectly under Windows.

So: does Time Machine do something unusual that makes a standard disk unsuitable?

Does anyone have a recommendation for an external disk that works reliably with Time Machine? Bear in mind I'm looking for something affordable - no exotic stuff please!


2011-07-25, 11:41
Why use Windows to partition / format?
On the Mac, disk utility will do the same and you can use the Mac OS Extended format which is recommended.

If you remove the drive from its USB shell and mount it on a computer via SATA or eSATA you should be able to access its RAID status and see if there is indeed a problem with the drive hardware. I've also seen finicky USB bridges, perhaps the disk case is responsible for issues.

Other than having the drive work every 15 minutes I don't think TM is overly stressful.
(My TM volume is an ext2 disk image file loop-mounted in a server, exported via NFS, reexported as a TM volume by a Linux VM running Netatalk... And it works nicely.)

2011-07-26, 01:30

This is probably obvious, but worth mentioning. It sounds as though this disk is used for occasional backups (plug it in, do a backup, disconnect it), rather than as a permanently connected backup drive. Keep in mind though that Time Machine likes to run frequent incremental backups, so if your daughter completes a backup and then leaves the drive connected, an hour later TM will start another (albeit small) backup. One possibility is that unplugging the drive during a backup might be causing problems. Make sure your daughter checks the little TM icon in the menu bar before disconnecting the drive - if the arrow is going round she should either wait for the backup to finish or cancel it before unplugging. Also make sure that she 'ejects' the drive before physically unplugging it.

I'd also echo the advice to use Disk Utility to format the drive as 'Mac OS Extended (Journaled)' - I don't profess to know all the details, but it seems likely that the OS will handle problems on the drive better if it's a native format.

2011-07-26, 06:43
Thanks for the replies.

Why use Windows to partition / format?
I did this because my daughter told me the Mac couldn't use the disk so I tried to recover it with the equipment I had available.

However, things have moved on a bit. I finally found this article: http://support.apple.com/kb/TS1550

The symptoms described seem to match my daughter's problems. I used my daughter's Macbook to reinitialise the disk with the GUID partition scheme and so far it seems to be OK.

Given that this is a known issue, I'm a little surprised that Time Machine doesn't check if the disk uses MBR partition types and issue a warning.