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macrumors member
Original poster
Mar 14, 2008
I've recently replaced the failing HDD in my iMac and restored from the Time Machine backup on my Synology NAS. I would like to keep that Time Machine backup intact for a little while, while I ensure I got everything, but I would also like to start a new backup. Every time, I try to start Time Machine again, it touches the old backup set. Fortunately, I've stopped it before it wiped any data, but how to I force Time Machine to start a brand new sparsebundle file? I've tried changing the name of the sparsebundle, as well as ownerships and permissions, and it always seems to find it and continue using the old backup set.

I can find all sorts of help about reconnecting to an old backup set, but nothing about disconnecting. Any ideas out there?

thanks in advance.


macrumors 65816
Apr 30, 2008
USA (Virginia)
You can probably do it with the “tmutil” command in, but it will take a bit of reading and understanding.

Sorry I am not at my computer right now, but you can open and enter “man tmutil” to display the help information for the command.

Hopefully somebody will post an easier way...
[doublepost=1545925006][/doublepost]Hmmmm. Looks like my last posting isn't useful; I'm at my computer now looking at the "tmutil" command and don't see anything there for what you want to do. In the parlance of the tmutil command, you want to create a new "backup disk image" (which is a .sparsebundle), and I don't see any subcommand to do that in tmutil. Sorry.

In theory you could just copy the old .sparsebundle from your NAS to a spare drive and then delete it from your NAS. But that could take a LONG time, assuming you even have the extra disk space somewhere!

Have you gone into TM preferences and tried the "Select Disk..." button? Maybe if you re-select your NAS drive it will start a new set of backups?

Remember, if you just go ahead and let TM continue to use the existing backup, all of your old files will still be there until that drive (actually, volume) gets filled up. At that point TM will delete the oldest snapshots. When an old snapshot is deleted, only files that DON'T exist in any more recent snapshots are deleted. You didn't mention how full that drive is that contains your backup.


macrumors Penryn
Feb 20, 2009
"How do I Force Time Machine to start a new backup?"

Why not erase the old one, and start over?
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