Time machine problem: two machines over network to one external hard drive

[Haberdasher]

I'm having trouble backing up with Time Machine.

Here's the setup:

1. Three, 1TB external hard drives in a concatenated software RAID. This means that they are treated as one large drive. There is no mirroring, no increased data rate, blah blah blah. It's just three hard drives in the place of one. I am aware that this means my backup is three times as likely to fail with the hardware, but that's OK.
2. These three are connected to a USB hub.
3. This hub is connected to a G5 tower. The G5 tower can back up to the concatenated drives (I'll call them just a RAID from here on), and also all additional external hard drives that I connect to the G5 tower have been backing up to the RAID no problem. This is great.

Here's the problem:

I'm trying to get two more computers to back up to the RAID wirelessly. I read a lot online about how this didn't used to be a supported feature (backing up to an external hard drive over a network with time machine), but that Apple has recently upgraded Time Machine to support this functionality.

The first computer I started with to try to backup over the network was a Macbook Pro, trying to get it to backup to this RAID. It can see the RAID over the network, mount it, copy files to it/read it, but CANNOT time machine backup to it. I select the network RAID as the backup device, hit "back up now," then get this message:

"The external volume cannot be mounted."

This is really bizzare, considering that it is mounted, and that I can copy to it. Just for your information, I have an airport extreme wireless network that has been working beautifully, no Keychain access issues, no 3rd party firewall, nothing. I've run through Applecare on this issue: the MacBook Pro has never done ANY time machine backup on the RAID, not even a partial one, so there's no dangling sparse bundle or backup folder or anything like that. All network permissions check out, etc. I've tried repairing the RAID with disk utility, as well as repairing permissions (although I have not done either of these things to the MacBookPro).

The latest thing I tried was plugging the RAID directly into the Macbook Pro. Here's where I got the first clue (at least I think so)...

Plugged DIRECTLY into the MacBook Pro, the RAID will mount, but the MacBook Pro WILL NOT backup to the RAID. It gives me the same message: the selected volume cannot be mounted. Again, this is strange considering that, just like when I am viewing the RAID over the network, plugged directly into the MacBook Pro the RAID will mount, I can read it, copy files to it, etc.

I have considered plugging the RAID into the Airport extreme directly, but first of all this would mean much slower transfer speeds with the G5 tower, which is a big issue considering the files I am backing up every day, and two, since it seems that the RAID won't be recognized by the MacBook Pro even when plugged in directly, I'm thinking that this is a more fundamental issue.

Any thoughts or ideas about how to try to figure this out would be greatly appreciated!

 

[danny_w]

My only thought would be the format of the RAID. I think that I read that TM requires a specific format on the target drive, and this may explain the TM mounting problems. I have a WD 750GB USB drive connected to my AEBS and formatted as HFS+/GUID that works great from several machines as a TM backup device.

 

[Haberdasher]

My only thought would be the format of the RAID. I think that I read that TM requires a specific format on the target drive, and this may explain the TM mounting problems. I have a WD 750GB USB drive connected to my AEBS and formatted as HFS+/GUID that works great from several machines as a TM backup device.

What's puzzling for me is that it backs up fine on the G5, but not the MacBook Pro.

It's also HFS+, journaled.

 

[danny_w]

What's puzzling for me is that it backs up fine on the G5, but not the MacBook Pro.

It's also HFS+, journaled.

Does it back up via TM on the G5? Is it GUID?

 

[Haberdasher]

Does it back up via TM on the G5? Is it GUID?

Yes, it is backing up to the G5.

I partitioned/formatted it on the G5, so that means it's not GUID, right? Do you think that's the issue?

 

[danny_w]

Yes, it is backing up to the G5.

I partitioned/formatted it on the G5, so that means it's not GUID, right? Do you think that's the issue?

I think that Leopard can format a partition as GUID even on a G5. You have to select "options" in Disk Utility when partitioning.

 

[Haberdasher]

I think that Leopard can format a partition as GUID even on a G5. You have to select "options" in Disk Utility when partitioning.

Why would GUID partitioning matter for time machine on the MacBook Pro?

 

[dfs]

Sparsebundles

If you solve this problem, you will then be confronted by another issue. When you back up multiple Macs to a networked volume, Time Machine creates so-called Sparsebundles (special disk images whose sizes can expand automatically) to contain the backup files it creates. Plenty of people, myself included, have experienced problems because if any of the contents of a sparsebundle become corrupted the thing ceases to work (some people have reported success in finding and eliminating the culprit, but it sounds like a lengthy and tedious job). So I decided that I couldn't entrust my data to sparsebundles and went back to hanging a separate h. d. off each (well, at lest both) of my Macs.