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View Full Version : Can SD! clone Time Machine backups.backupdb


Al_from_Ottawa
11-28-2015, 02:43 PM
Trying to clone a time machine drive to a new larger disk. First tried to do it the way Apple suggests by turning off Time Machine, turning on Owners in the destination, and doing a drag copy of backups.backupdb in the finder. After an hour it was still at about 400K files "preparing", with the file count increasing glacially slowly. It looked as if it might take over a day before it even started copying. Seemed really weird for it to be so slow with a USB3 source drive.

So I decided it was worth trying SD! (erase and clone).

After 30 minutes SD! is showing about 300,000 of 5.8 million files copied with an effective copy speed around 40 MB/sec.

I know from having just cloned my boot drive that it contains around 2 million files. I can't understand the number 5.8 million. It suggests that on average there are 3 versions of every file in the time machine backup (1 TB backup for a 0.5 TB boot drive). That seems high to me, but maybe it is accurate. SD! cannot be getting confused by the multiple links to each file in different hourly backups, since the number of apparent file instances would surely be orders of magnitude larger still.

I plan to let the cloning complete and see whether the total disk space in the clone is similar to the original. And see whether time machine will accept it as a valid backup volume and not try to back everything up again. Of course if SD! is getting confused by some of the hard links, and creating duplicate files, it could easily run out of space even though the destination is larger than the source.

Can you offer any illumination about how SD! deals with the hard links? Or why Finder Copy is so totally slow? I'm curious.

dnanian
11-28-2015, 05:54 PM
There are millions and millions of files and links. Each "identical" file on a subsequent backup is a hard link. We track them all, to files and folders, and reproduce them properly on the copy.

It takes along time. 5.8 million is totally normal...and does not suggest 3 versions. Quite the opposite.

I don't know why Finder is slow, because I don't know what it's doing (although I believe it "unrolls" all the links). We're slow because of all the bookkeeping...of which there's a ton, along with the file I/O necessary.