Disk Utility changes

[bripakes]

Apple has posted the iMac (intel) service manual (to Service Source). In reading parts of the manual there are discussions regarding an updated version of Disk Utility that must be used. Can someone enlighten me as to why? (the manual suggests that a target-booted iMac HD that has multiple partitions will appear as 1 partition when mounted to a PPC Tiger box)

[maccanada]

The Intel Macs use something called GPT (GUID Partition table), which is a major advance over the old method of Master Boot Records (MBRs).

Again from kernelthread – the advantages of GTP:
64-bit LBA (thus, disk offsets are 64-bit).
Supports many partitions (without resorting to nesting schemes like “extended” partitions).
Uses version number/size fields for future expansion.
Uses CRC32 fields for improving data integrity.
Each partition contains a 36 Unicode character human readable name.
Uses a GUID and attributes to define partition content type (note that tagging each partition with a GUID makes relocation easier).
Uses a primary and backup table for redundancy.

This last point is a huge improvement – while not what I’d call frequent, I have experienced corruptions of the MBR on PC’s.

And this is taken from TechNet:
The GUID partition table (GPT) disk partitioning style supports volumes up to 18 exabytes in size and up to 128 partitions per disk, compared to the master boot record (MBR) disk partitioning style, which supports volumes up to 2 terabytes in size and up to 4 primary partitions per disk (or three primary partitions, one extended partition, and unlimited logical drives). Unlike MBR partitioned disks, data critical to platform operation is located in partitions instead of unpartitioned or hidden sectors. In addition, GPT partitioned disks have redundant primary and backup partition tables for improved partition data structure integrity.”

Anyway, you’ll need to have the version of disk utility that allows for creation and reading of GPT’d drives.

~Ian

[komakino]

That kernelthread article is excellent. I can’t wait for his book to come out.

Because the Intel Macs use EFI instead of Open Firmware and EFI can’t boot Apple Partition Map formatted drives (apparently) that means that in order for a disk to be bootable it has be be formatted with a GPT partition table.

Which begs the question, can PowerPC Macs boot from GPT formatted disks? It looks like they cannot. This means that at least for now it will not be possible to have one physical disk that can boot PowerPC and Intel Macs, even if the disk is partitioned with a PowerPC OS X and an Intel OS X.

[maccanada]

Right now for Netboot you will need 2 images. One for Intel and one for PowerPC. The same will hold true, I guess, for any boot drive.

However, please feel free to test! 10.4.3 has the option of creating a GTP partition scheme – man diskutil and look for GPTFormat. Current Macs can create and mount drives created with a GTP scheme – I’ll test booting when I get chance, but I’m not holding my breath 🙂 Leopard will likely be the first Universal OS

~Ian

[komakino]

I will do some testing, however I cannot find any mention of ‘GPTFormat’ or ‘GPT’ or ‘GUID Partition Table’ in the man page for diskutil on my 10.4.4 system. I checked another 10.4.4 system and a machine running 10.4.3 Server and the man pages for diskutil are identical. No gpt mentioned anywhere in them.

However all of these systems do have the ‘gpt’ command installed which looks like it is the right tool for the task.

-Chris

[sphns]

$ diskutil partitiondisk
Disk Utility Tool
Usage: diskutil partitionDisk [Mount Point|Disk Identifier|Device Node]
numberOfPartitions <OS9Drivers, APMFormat, MBRFormat, GPTFormat>
<part1Format part1Name part1Size> <part2Format part2Name part2Size>
<part3Format part3Name part3Size>
(Re)Partition an existing disk. All volumes on this disk will be destroyed.
Ownership of the affected disk is required.
Format is the specific filesystem name you want to erase it as. (HFS+, etc.)
OS9Drivers specifies that an Apple Partition Map should be used, and laid
out in a manner compatible with Mac OS 9.
APMFormat specifies that an Apple Partition Map should be used.
MBRFormat specifies that the partition map should be written in DOS
compatible format.
GPTFormat specifies GUID Partitioning Scheme.

I wouldn’t recommend using the gpt tool, it doesn’t lay out the disk in the manner required by the OS (i.e. it doesn’t automatically create a ESP, which is required in order to install the OS).

[sphns]

[QUOTE BY= komakino] That kernelthread article is excellent. I can’t wait for his book to come out.

Because the Intel Macs use EFI instead of Open Firmware and EFI can’t boot Apple Partition Map formatted drives (apparently) that means that in order for a disk to be bootable it has be be formatted with a GPT partition table.

[/QUOTE]

The EFI in the Apple machines can boot Apple Partition Map formatted drives. Look at the Install DVD that ships in the box. It’s just a straight APM disc.

You can’t however, install on any partition format other than gpt. So for all intensive purposes, you have to partition your drives (internal, external Firewire or USB ) as gpt in order to install the OS.

[Author]

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