Mac – does Time Machine estimate a 109GB backup size, but then need 235 GB

time-machine

I'm running Time Machine on a new NAS. Until today, I used to run it on an USB drive. I am reusing the old job using the new 10.8 feature that allows me to add new backup targets.

When I configure the backup job in the system settings – there are some things like VMs that I want to exclude – Time Machine estimates the backup size to be 109 GB.

When I start the backup, however, it talks about 235 GB. I don't like this, as I don't want to litter the NAS with unnecessary data.

Is it normal that Time Machine shows such a huge difference between the System dialog, and the actual backup?

Best Answer

This discrepancy is odd - most of the time when people see more than a 25 GB error, it's with Time Machine over-estimating the space that will be used rather than under-estimating. You might be on to something where there is abug in calculating things with multiple backup targets - I've not seen that configuration start to misbehave yet - so you might be one of the lucky few to see how things break under that setup.

If you can make this happen repeatedly, I'd submit a bug (or at least poke around) by running the tmdiagnose tool to collect data on the estimates and actualities.

Also, the Backuploupe tool is amazing at getting at space usage and estimate oddities when you use Time Machine. It's not able to catalog both destinations simultaneously yet - but seems to work well enough on Mountain Lion that I still use it regularly.

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MacOS – How to backup NAS using Time Machine

I wouldn't use Time Machine for this, it is best at backing up your local Mac. The NAS you have has a built in backup function that can use a local USB drive or a network share (as well as other options). So if you want to backup the NAS to a drive mounted on your Mac just set the share up on the Mac then configure the NAS to backup to that share on a schedule. If you really want to use Time Machine you would have to mount the NAS or more likely specific directories on the NAS then include those in Time Machine on the Mac, This article gives good info on backing up several types of network shares to your Mac thru time machine: http://lifehacker.com/5685547/how-to-set-up-time-machine-to-back-up-to-a-networked-windows-or-linux-machine

Mac – Deleting all but the most recent Time Machine backup

Assuming OSX 10.8 or later, you could use a combination of find and tmutil

tmutil delete <path> will remove the snapshot at <path>

while

find /path/to/backups/ -maxdepth 1 will list all of your backup snapshots. The last one ( Latest ) is a link to the latest one. You can be a little creative and use find /path/to/backups -name 2\* -maxdepth 1 to list only the "real" directories (all the dates which start with 2014, etc). And, finally, (thanks to this link) you can get a list of all but the last snapshot:

find /path/to/backups -name 2\* -maxdepth 1 | sed \$d

Best Answer

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