[X4U] Disk Utility on Panther and Tiger

[David Ledger]

>From: Wayne Clodfelter <wayne at troutnc.com>
>>>  From: Wayne Clodfelter <wayne at troutnc.com>
...
>>>  Oops! What if DU on Panther is not compatible with Tiger?
>>>  It probably isn't--though I have not seen a statement to that effect
>>>  anywhere.
>>>
>>>  ONE, Disk Utility under a superseded version of OS X should not even
>>>  be able to verify/repair a system disk of a later release unless it
>>>  is compatible. ...
>>>
>>>  TWO, it should be possible for the latest version of Disk Utility to
>>>  be installed/copied over to boot volumes containing earlier OS X
>>>  releases.
...
>>>  Of course, this raises the question whether the latest release of
>>>  Disk Utility is always backwards compatible with earlier OS X
>>>  incarnations. Is this true or not?
>
>I have a few problems with what you have written.
>>
>>  ONE.  Filesystem repair utilities look at filesystems; that is they
>>  see a partition as an array of bytes that must conform to some rules.

>So, if the "rules" are different between Panther and Tiger, DU will
>do what? Recognize that the file system IS different and do nothing,
>or try to bend the file system to ITS rules?

The rules are those that define the filesystem, most likely HFS+. 
This doesn't change between OS revisions without us being told. There 
are also rules that define the layout of partition maps and the like. 
The filesystem rules are similar in nature, but vastly more complex. 
The global disc allocation table must match that allocated to 
objects, block pointers must point to sensible places ... all that 
sort of thing.

Later versions of utilities may well be better at doing the job, but 
what they are trying to check is relatively constant.

>>  They do not look at files. Examining files needs a whole section of
>>  the OS to support it, and that may not be available. When disc
>>  utilities start looking at the contents of a disc and then deciding
>>  that the data indicates that it shouldn't repair it, we've lost
>>  something - even if it would protect you from Norton.

>I don't know what this is all about. I didn't mention file repair.

Sorry, I wasn't clear. I meant that it would have to read files on 
the filesystem the determine the release of OS living on it if it 
were going to implement:  ">>> Disk Utility under a superseded 
version of OS X should not even be able to verify/repair a system 
disk of a later release unless it is compatible."

>>  If the filesystem it's pointed at is incompatible it will notice;
>>  if it's just created by newer software it may not notice, or be
>>  written to ignore the fact.
>Which is it? Will it notice or not? You can't say it will notice if
>it is incompatible but it won't notice if the incompatibility is
>caused by being newer than the file system it is analyzing.

In the case of Disk Utility, it is compatible with HFS, HFS+, UFS, (+ 
various PC filesystems??). Present it with a VMS filesystem or a raw 
Oracle partition and it will notice it's different (second hand drive 
in a FW case). It probably can't tell the difference between HFS+ 
created at various OSXs (unless Apple put some marker in it when you 
upgrade your OS) other than maybe the presence of Journaling. Disk 
Utility will probably recognise whatever it was that preceded HFS on 
the Mac (can't remember what it was called), but may well just refuse 
to process it. The same with some PC formats.

It's rather like programmatic validation of HTML. There are programs 
that will check the HTML correctness of a web page, that work whether 
the page text is English, French or Japanese. They don't verify that 
the words make sense. They don't look at the words and decide 'this 
page has factual errors - I won't verify it'. Disc utilities don't, 
and shouldn't, say 'some of the files on this disc are from a later 
copy of the OS - I won't fix it'.

>>  TWO.  From what others have said here you can use later versions of
>>  Disk Utility  to repair discs created by older systems, but I don't
>>  know how far back that goes. 10.3 Disk Utility worked with my OS9
>>  partition on my G4. That partition was loaded while booted from the
>>  OS9 install CD. Havn't repaired that partition since I put Tiger on
>>  it last weekend (at last - using FireWire disk mode from my PB). If
>>  a newer utility runs on an older OS it means that the library calls
>>  have all resolved and so it should be fine.

>So if DU from Tiger will run while booted from Panther, it means that
>the library calls have all been resolved and so it should be fine? I
>don't think so.
>I believe that DU on a Tiger boot volume will run while booted in
>Panther, but it cannot be used to verify/repair the same Tiger volume
>because that volume contains a running app, which is DU, itself.

Well, it can verify the boot volume and it can repair another volume. 
That's a limitation that would also apply if it were a Panther DU.

David


-- 
David Ledger - Freelance Unix Sysadmin in the UK.
Chair of HPUX SysAdmin SIG of hpUG technical user group (www.hpug.org.uk)
david.ledger at ivdcs.co.uk
www.ivdcs.co.uk