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jerrykrinock 04-02-2010 01:31 PM

Time Machine Copy
My Time Machine drive became unwritable, so I bought a new drive and copied data from the unwritable drive to the new drive using the procedure given here: It worked nicely. After the copy, I told Time Machine to start using the copied drive, and Time Machine picked up where it had left off. My old backups as well as new backups are all available in Time Machine.

I'm wondering why it took 22 hours to copy 220 GB of Time Machine backups, though. This is indeed about the same as the "effective transfer rate" of about 3 MB/sec which I recall being displayed by SuperDuper! But on the box of the drive is written "transfer data at up to 480 Mb/sec", which is 60 MB/sec, which means that 220 GB = 22000 MB should have taken 6 minutes. Allowing for reasonable overhead, I expect maybe 10 minutes. 22 hours is 130 times longer than my calculation of 10 minutes. Why? (Time Machine takes a similarly long time to do its first backup also.)

Also, a bonus question. In the interim, I was using another volume for Time Machine. So now my new Time Machine volume is missing several days which are on my interim Time Machine volume. Is there any way to merge Time Machine data from my interim Time Machine volume back into my new Time Machine volume? I suspect that simply dragging the dated folders from the Backups.backupdb directory wouldn't work.

dnanian 04-02-2010 01:36 PM

Well, because "wire speed" of a USB drive is talking about writing a single stream, unidirectionally, with no OS overhead at all. Just not going to happen... we're reading/writing tons of teeny files and attributes, using an OS which has its own overhead, etc.

No, no way to merge the backups - don't even try.

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