Time Machine/HFS question

Christopher Wolf cwolf at mac.com
Tue Mar 4 20:41:46 PST 2008 

On Mar 4, 2008, at 10:57 PM, Justin C. Walker wrote:

> Thanks, Chris and David,
>
> On Mar 4, 2008, at 15:25 , Christopher Wolf wrote:
>
>> On Mar 4, 2008, at 5:41 PM, David Mackler wrote:
>>> On Mar 4, 2008, at 1:59 PM, Justin C. Walker wrote:
> [snip]
>>>> Now, I mount the device, Time Machine remains 'off', and when I  
>>>> turn it on, I get a drop down window where, presumably, the  
>>>> available drives are given.  This window is empty, and there's  
>>>> nothing in the logs to indicate what's happening (other than the  
>>>> mounting of the drive over AFP is logged).
>>>
>>> There is clearly an asymmetry with Time Machine. The ".backupdb"  
>>> is created for a locally attached drive, and the ".bundle" is  
>>> created for a network attached drive.
>>
>> The .backupd folder needs to live on a Leopard HFS+ filesystem with  
>> support for directory hard-links, extended attributes and ACLs.
>>
>> However, if a volume is accessed over the network (even if it is  
>> formatted HFS+) the client machines don't see it as an HFS+ volume  
>> but rather as an AFP volume (which does not support directory  
>> hardlinks or extended attributes). To get around this Time Machine  
>> creates a .sparsebundle disk image on the AFP volume containing a  
>> HFS+ filesystem. Time Machine creates its .backupd structure on the  
>> HFS+ filesystem contained within the mounted disk-image in that case.
>
> I think I'm still puzzled :-}
>
> From your first mail, Chris, it sounded like access to remote drives  
> is possible only when the server is 10.5.

> In my setup, there are two 10.4 systems, including the main server  
> hosting the firewire drive, and one 10.5 system.

Time Machine backups to remote drives are only supported when the  
server is running 10.5. If you are trying to back up to a 10.4 system  
that is not a configuration which is supported. The Time Machine  
preference pane should not allow you to backup to a AFP volume hosted  
by a 10.4 server. (And it sounds like that is what you are now seeing.)

If somehow Time Machine got confused and was trying to back up to a  
10.4 server (and it sounds like perhaps that is what was happening to  
you) then the results would be unpredictable. I could only speculate  
as to how Time Machine might get confused like that... perhaps a 10.5  
server was replaced with a 10.4 server with the same hostname and  
sharing the same backup drive? Perhaps one of the various hacks  
circulating on the internet was used to bypass the checks which  
prevent backing up to a 10.4 server? Perhaps a drive which was  
originally configured for local (directly attached) backups was moved  
to a server and somehow Time Machine is still finding it and trying to  
use it?

> The only way the ".backupdb" could have been set up is when the  
> firewire drive was mounted on the 10.4 system, correct?

The .backupdb directory should have only been created when a computer  
was backing up to a directly attached firewire drive, not when the  
computer was backing up over a network.

> I only physically attached this drive to the 10.5 system for a few  
> brief periods, one begin before 10/29 (when I was trying to get the  
> drive to work :-}), and once a couple of weeks ago (post 10.5.2  
> upgrade).  There wasn't enough "connect" time in the first case to  
> create the 6 "2007-10-29-*" directories (they were apparently  
> created over a period of about 5 hours, based on timestamps).  Is  
> there a way to verify which system the drive was connected to when  
> these directories were created (memory being somewhat fallible :-})?

Each of the 2007-10-29-* directories represent an hourly snapshot  
created by Time Machine. Those directories should be contained within  
another directory which is named with the name of the machine that was  
being backed up. If things were functioning as expected then those  
snapshots must have been created while the drive was attached to that  
machine.

> As for the "sparsebundle", it is not a disk image, it's a real  
> directory.

The fact that it's a directory does not preclude it from being a disk- 
image. It's actually a bundle. Disk images come in a variety of  
forms... the traditional ".dmg" images use a single non-expandable  
file. A sparsebundle is a different type of disk image which uses a  
bundle (directory) instead of a single file to store it's data. (The  
hdiutil man page elaborates a bit on the different types of disk  
images).

> Based on the timestamps on the "bands" in this directory, it had to  
> have been connected to a 10.5 system for quite a spell, if I  
> understand your comment (it can only be served from a 10.5 system,  
> and is used only to handle remote 10.5 clients).  Is that correct?

>
> If so, I'm really confused, because this firewire drive was  
> physically attached to the Mac Pro (10.4) during the period that  
> these "bands" were created.  I think I only once moved the drive to  
> the laptop (10.5), and then only briefly.

I'm saying that Time Machine *should* only allow you to configure  
backups to a 10.5 AFP server. If somehow you ended up backing up to a  
10.4 server then the backups may have appeared to be working and the  
disk-image could have been updated while being served from the 10.4  
server. However, I would not trust that backed up data. And it is not  
surprising that Time Machine is no longer working in that  
configuration and will not let you configure the 10.4 server as a  
backup destination anymore.

> Again, thanks for your explanations.  Is any of this documented?  I  
> checked ADC, but nothing obvious popped out (overviews and API  
> discussions were all I saw).

The feature page at Apple's site <http://www.apple.com/macosx/features/timemachine.html 
 > states:
"Time Machine can also back up to another Mac running Leopard with  
Personal File Sharing, Leopard Server, or Xsan storage devices"

And this kbase article <http://docs.info.apple.com/article.html?artnum=306833 
 > states:
"Time Machine can back up to another Mac running Leopard with Personal  
File Sharing, or to a Leopard Server volume, or an Xsan s
storage device."

- Chris

>
>
> Justin
>
> --
> Justin C. Walker, Curmudgeon-At-Large
> Institute for the Enhancement of the Director's Income
> --------
> Experience is what you get
>  when you don't get what you want.
> --------
>
>
>
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