TimeMachine Backup through another Mac!

Yes, you can do this. I'm not sure if it will continue to use the backup you already started, but I've heard that it can.

Make sure the drive is shared out so that your user on the MBP can read/write to it. Your iMac will show up in the sidebar of the MBP under SHARED. Click on it and it will try to connect initially with your current login on the MBP. If you need to use a different login, use Connect As… after disconnecting the initial login. Once connected, you should see the disk in the Finder window. Double-click on the disk to mount it on your MBP.

You should be able to select that disk as the backup destination in TM. TM identifies backup sets using the computer's MAC address. Since you were hard-wired to the initial backup, it may be the Ethernet MAC, but when you connect wirelessly, it will only see the Airport MAC address, I think. There are ways to change that ID info for the backup. Search for Time Machine and Change logic board.

If you can't choose the disk in TM, go to the Finder window that has the hard disk open and grab the little icon in the title bar of the window. Drag it to the sidebar and drop it in the DEVICES section. You should now be able to select it.

Once TM completes its initial backup, you can eject the disk and TM will automatically mount the disk when needed. If you are away from home, it will still attempt to connect if you are connected to any network. You may want to turn TM off for that time and don't forget to turn it back on. I'm not sure what number of failed backups or time period triggers a Deep Traversal, but at some point of non-connect to the drive, TM will want to do a complete scan of the drive to figure out what has changed. This will take a while, but will continue the backups normally after that.

Barney-15E wrote:
Yes, you can do this. I'm not sure if it will continue to use the backup you already started, but I've heard that it can.

Hi, Barney,

No, Time Machine will start a whole new "set" of backups. Time Machine always stores it's backups in a Backups.backupdb folder, but when done over a network, that folder is placed inside a +sparse bundle.+ The two are not compatible.

I'd also advise partitioning the disk, so TM on the directly-attached Mac has it's own, exclusive space. See #4 in the Frequently Asked Questions *User Tip,* also at the top of this forum, for info and a reference to detailed instructions.

The existing set of directly-made backups has the backups for both Macs. You can see the "other" set via the Browse option (#17 in the FAQ Tip). Once you're sure you don't need them any more, you can delete all backups of the MBP -- see #12 in the FAQ.

Pondini wrote:
No, Time Machine will start a whole new "set" of backups. Time Machine always stores it's backups in a Backups.backupdb folder, but when done over a network, that folder is placed inside a +sparse bundle.+ The two are not compatible.

I thought it also created as sparse bundle when multiple computers were backed up to the same drive, which I thought the OP mentioned. I was going to add "if it is a sparse bundle image," but did not go back and edit it. Will it still not work if it is already a sparse bundle disk image?

Barney-15E wrote:

Pondini wrote:
No, Time Machine will start a whole new "set" of backups. Time Machine always stores it's backups in a Backups.backupdb folder, but when done over a network, that folder is placed inside a +sparse bundle.+ The two are not compatible.

I thought it also created as sparse bundle when multiple computers were backed up to the same drive, which I thought the OP mentioned.

No, if done while directly-attached, they're all included in the same Backups.backupdb folder.

The structure is like this:

Backups.backupdb
..Name of first Mac
....Backup date & Time
......Hard drive/partition
....Backup date & Time
......Hard drive/partition
....(etc)
..Name of second Mac
....Backup date & Time
......Hard drive/partition
....Backup date & Time
......Hard drive/partition

You'd think you could copy (or delete) just the folder for one Mac, but the result is corruption.

I was going to add "if it is a sparse bundle image," but did not go back and edit it. Will it still not work if it is already a sparse bundle disk image?

If it's a sparse bundle, there's one per Mac, each with it's own Backups.backupdb folder. Oddly enough, it does include the Computer Name folder at the top level.

I've never even seen any speculation as to why Apple does it this way, but there must have been a good reason, or they wouldn't have written two sets of code.

This thread has helped me set up just what you want to do. I learned the hard way that I could not use Time Machine to backup to a directly connected drive (Firewire 800) for the first backup and then do wireless incremental backups to the same drive partition later. My first backup took about 50!! times longer via WiFi, but incremental backups are fast enough at least so far.

My question for this thread is what about recovery? Using Time Machine for a few files damaged or erased accidentally should work fine over WiFi, but what happens if I have to reformat or replace the drive on my MacBook Pro? I believe the utility on the OSX startup disk to load your most recent backup to your virgin MBP hard disk, will only work if the backup drive is directly connected to the target machine. If that is so and supposing the backup drive is directly connected, will the utility on the startup disk be able to access a backup file originally transferred via WiFi? If the answer is no, I will be looking at another solution...

I don't know the answer to this question? Do any of you experts?

Paamul wrote:
This thread has helped me set up just what you want to do. I learned the hard way that I could not use Time Machine to backup to a directly connected drive (Firewire 800) for the first backup and then do wireless incremental backups to the same drive partition later. My first backup took about 50!! times longer via WiFi, but incremental backups are fast enough at least so far.

If you're using a Time Capsule or external HD connected to an Airport (not officially supported), you can do the first backup much faster while connected via an Ethernet cable. If you're backing-up to a shared disk on another Mac, I believe you can connect the two via Ethernet, also, but I don't know for sure.

My question for this thread is what about recovery? Using Time Machine for a few files damaged or erased accidentally should work fine over WiFi, but what happens if I have to reformat or replace the drive on my MacBook Pro? I believe the utility on the OSX startup disk to load your most recent backup to your virgin MBP hard disk, will only work if the backup drive is directly connected to the target machine.

You can use WIFI (but yes, it's much slower that way),

If that is so and supposing the backup drive is directly connected, will the utility on the startup disk be able to access a backup file originally transferred via WiFi?

If you're talking about an external normally connected to an Airport or Time Capsule, or another Mac via sharing, yes, it will find the backups if attached directly. If a Time Capsule's internal HD, you can connect via Ethernet cable.

Thanks Pondini,

That answers all my questions and more! Thanks for covering all the options. I had not thought about going Ethernet via my iMac.

I have a 2nd HD in a MacPro (running 10.5.8) that I have successfully used to back up the MacPro as well as a new iMac 27". The HD is not partitioned, but properly created separate file sequences for each machine. But, backing-up wirelessly can be very slow.

How can I back up using a Firewire800 connection, being sure to bypass the wireless method (both computers are shared)? I thought the firewire worked on one occasion as the transfer went very quickly, only to find that Time Machine seems to hunt for the Wireless connection first.

Joel-Long Island wrote:
I have a 2nd HD in a MacPro (running 10.5.8) that I have successfully used to back up the MacPro as well as a new iMac 27". The HD is not partitioned, but properly created separate file sequences for each machine. But, backing-up wirelessly can be very slow.

How can I back up using a Firewire800 connection, being sure to bypass the wireless method (both computers are shared)? I thought the firewire worked on one occasion as the transfer went very quickly, only to find that Time Machine seems to hunt for the Wireless connection first.

Give the F/W disk a different name (for your reference), then specify that as your backup disk in TM Preferences > Select Disk.

If that doesn't work, and TM keeps trying to back up to the other one, the preferences file is probably corrupted. Do a "full reset" per #A4 of the Time Machine - Troubleshooting *User Tip,* also at the top of this forum.

You can alternate between two disks, whether they're local or on a network, but you must tell Time Machine which one to use each time you switch.