Time Machine won't show my network backup drive

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Level 1

71 points

Time Machine won't show my network backup drive

Time Machine on my MacBook Pro has been backing up to a sparse image on my iMac's TM backup drive since Yosemite (10.10). I don't recall touching the MBP's Time Machine setting when I upgraded to El Capitan (10.11) and Sierra (10.12).

Then, on May 18, I changed the router on my LAN. This resulted in my iMac (still running Yosemite) getting assigned a new fixed IP address.

When I discovered Time Machine had not backed up since May 18, I checked Time Machine preferences. Select Backup Disk still showed the iMac's TM drive, with the old IP address. I deleted the drive so that I could reselect it at the iMacs new IP address. But after mounting the iMac's shared TM drive, "Select Backup Disk..." shows only one choice: "Other AirPort Time Capsule"

Another discussion about a problem with network backup on Sierra recommended resetting the iMac's SMC and PRAM. That didn't help.

Why won't Sierra's Time Machine let me reestablish a network backup that has been working fine for a least a couple of years?

-- Ward

MacBook Pro, null

Posted on May 28, 2017 9:31 PM

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Answer 1

John Galt

Level 10

156,704 points

May 29, 2017 5:36 PM in response to Ward Clark

Thanks. You may wish to refer to If you can't back up or restore your Mac using Time Machine - Apple Support.

Is that iMac running macOS Server? That's required to use it as a host for Time Machine backups.

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Answer 2

John Galt

Level 10

156,704 points

May 29, 2017 7:27 PM in response to Ward Clark

For a long time Apple was frustratingly vague regarding the devices Time Machine will support. Apple's Support documents used to say that the Mac hosting the TM backup had to be running AFP, for which there have been a number of poorly implemented non-Mac open source imitations of it that were never supported, and have never been reliable. Then, they changed their support documents to indicate a Mac "on your network" can host the TM backup drive. Later, they quietly changed their documentation to specifically indicate that Mac must be running macOS Server.

So you're right, what you had been doing may have been OK in the past, but it's not any more, and I don't know exactly when that change occurred.

At this point, It appears the most practical way forward is to purchase a bus-powered external drive for local backup. Disconnecting and reconnecting the external drive would be a hassle if the MBP travelled.

It's not as bad as you may think. On portables, Time Machine creates "local snapshots" that effectively serve as backups when the backup device is not connected or otherwise available. Its limitations are obvious: they cannot be used to restore an entire system, and they won't help if the source volume becomes corrupted or lost. And, they will only be created as long as sufficient space exists on that volume. When that space becomes insufficient and the Mac needs more room to work, those "local snapshots" become the first candidates for deletion.

About Time Machine local snapshots - Apple Support

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Answer 3

Ward Clark Author

Level 1

71 points

May 29, 2017 6:15 PM in response to John Galt

John, I see the official word from Apple is Time Machine on my MPB can no longer use my iMac's TM HD as the backup device.

Based on my recent experience, the reality is ...

Time Machine on my MPB cannot Select my iMac's TM HD as the backup device because the iMac is not running OS X Server.
If Time Machine on my MPB was configured in an earlier OS X release, Time Machine can backup to my iMac's TM HD. As I mentioned in my original post, Time Machine was backing up hourly until May 18, when I changed my router.

At this point, It appears the most practical way forward is to purchase a bus-powered external drive for local backup. Disconnecting and reconnecting the external drive would be a hassle if the MBP travelled. Fortunately, these days it spends 98% of its time living in my home theater.

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Answer 4

John Galt

Level 10

156,704 points

May 28, 2017 11:59 PM in response to Ward Clark

Then, on May 18, I changed the router on my LAN. This resulted in my iMac (still running Yosemite) getting assigned a new fixed IP address.

That doesn't make a lot of sense to me. A fixed IP address is fixed. It doesn't get assigned by a router.

The Mac's IP address has no bearing on TM's function though; as a client on your LAN it can be assigned any IP address on its subnet, or you can specify a static IP address. What Time Machine needs is the IP address of the Time Capsule or AirPort Extreme hosting the TM backup drive so that it can find it. If you don't know what it is launch AirPort Utility and select the device. Its IP address will appear.

Another discussion about a problem with network backup on Sierra recommended resetting the iMac's SMC and PRAM. That didn't help.

It won't help unless the iMac is hosting the TM backup drive, in which case it might help. Otherwise it's unrelated.

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Answer 5

Ward Clark Author

Level 1

71 points

May 29, 2017 8:01 AM in response to John Galt

John Galt wrote:

Then, on May 18, I changed the router on my LAN. This resulted in my iMac (still running Yosemite) getting assigned a new fixed IP address.

That doesn't make a lot of sense to me. A fixed IP address is fixed. It doesn't get assigned by a router. ...

My iMac was connected to the old router using DHCP with a fixed address. When Time Machine's settings on the MBP showed the iMac's TM HD, the fixed IP address appeared in small text below the drive name. I assume that IP address was to identify the LAN location of the drive; the iMac's name was not shown.

I do not have a Time Capsule or Airport Extreme. Before the router change, my MBP had been backing up to a sparse image on my iMac's TM HD over file sharing.

-- Ward

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Answer 6

Ward Clark Author

Level 1

71 points

May 29, 2017 7:47 PM in response to John Galt

Thank you, John, for your scholarly tutorial. I'm saving a permalink for passing along to others.

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