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Using multiple backup disks for Time Machine is perfectly save
Authored by: palahala on May 20, '10 10:42:34PM

I think you will find that A is not on the TM2 drive.

No, that it's NOT true.

In the comments in the other thread you'll also find references to Ars Technica, which has has some nice technical insight about Time Machine and how it relies on fsevents. And you'll read that Time Machine stores the last known event ID on the backup itself, in an extended attribute com.apple.backupd.SnapshotVolumeLastFSEventID.

Hence, Time Machine knows exactly when the last backup for a certain backup disk was created. So: unless file A is deleted from the filesystem very soon, you'll find it on both backup disks.

In your case, something else must have gone wrong.

Edited on May 20, '10 10:47:06PM by palahala


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Using multiple backup disks for Time Machine is perfectly save
Authored by: aubreyapple on May 21, '10 10:16:55AM

Oddly, since no one knows what that 'other thing' could be that went wrong, I suspect it goes wrong for lots of people so the caution still applies. IMHO.



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Using multiple backup disks for Time Machine is perfectly save
Authored by: palahala on May 21, '10 12:57:56PM

Not too odd to me, as it's really just not how fsevents works, and there's no reason to suspect Apple would stop using fsevents to determine what needs to be written to the backup.

So, care to tell us why you needed a full restore a few days after the backups, for which you claim Yes the pictures would still have been there on May 18th when the May 18th (TM1) backup was done? Maybe this actually calls for a high priority bug report then!



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Using multiple backup disks for Time Machine is perfectly save
Authored by: chucky23 on May 22, '10 07:42:01AM

Short version for folks arriving late to the conversation:

- palahala is correct.
- aubreyapple doesn't have the slightest clue what he's talking about.

Apple explicitly supports using multiple TM destinations. This hint is safe in that regard.



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Using multiple backup disks for Time Machine is perfectly save
Authored by: aubreyapple on May 22, '10 07:51:50PM

Well, you are right. I cannot reproduce the problem... not to say it did not happen to me, it did.

I still recommend caution.

So, chucky23, can you point to where Apple explicitly supports multiple destinations?

Thanks.

Edited on May 22, '10 08:00:09PM by aubreyapple



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Using multiple backup disks for Time Machine is perfectly save
Authored by: Tantali on Jun 09, '10 09:08:16AM

I've used this script for nearly half a year and haven't encountered any problems with it, except for an occasional reluctance to start backing up (which is immediately solved by manually telling it once to start a backup)

Edited on Jun 09, '10 09:15:48AM by Tantali



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