InformIT: Mac OS X Unleashed > Preparing Your Drive for Mac OS X

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Preparing Your Drive for Mac OS X

If you've made the decision to move forward with the installation of Mac OS X, you'll need to prepare your hard drive for installation. Mac OS X is very flexible in the possible system configurations allowed, and supports multiple partitions and both UFS and HFS+ out of the box.

Simple Upgrade from Mac OS 9.x

Determining the best configuration depends entirely on your needs. The simplest path to Mac OS X, while maintaining your current system software setup, is to upgrade to Mac OS 9.x9.x, and then perform the OS X installation. Apple recommends this approach only if you have existing data and cannot start from scratch.

If you are using Mac OS 8.5 or earlier, you will need to purchase the full Mac OS 9 CD and perform the upgrade like you normally would. Mac OS 9.x is a free update to 9.0 and is available for download from Apple's Web site (http://www.apple.com/).

Note

Systems earlier than 9.x, as long as they are running on a Mac OS Extended file system (HFS+), can have Mac OS X installed, and upgraded to 9.x at a later date. You will not be able to run Classic applications, but you will be able to access all the data files on your drive. If you are running any system using the base HFS file system, you will have to reinitialize your system as HFS+ or use a utility such as Alsoft's PlusMaker (http://www.alsoft.com/PlusMaker/support.html) to convert your existing data.

Any system that has been upgraded to Mac OS 9.x is ready to run the OS X installation, with a few minor exceptions. Due to differences in the drive controllers, the following machines might require special preparations:

PowerBook G3 Series
Power Macintosh G3 Desktop
Power Macintosh G3 Mini Tower
Power Macintosh G3 All-in-One
Macintosh Server G3
iMac 233MHz (Rev. A & B)
iMac 266MHz (Rev. C)
iMac 333MHz (Rev. D)

If you are using one of these machines, you might find that Mac OS X does not allow you to select your boot drive during the installation procedure. If this is the case, and you have the prerequisite 1.5GB of available space, the problem lies with your disk partition layout, not the install program.

What Is Partitioning?

Mac users don't usually have to worry about partitions, and might not be familiar with the term. A partition is a logical division on a piece of storage medium—usually a hard disk. To the computer, these divisions appear to be separate disks and each can be formatted with a different file system. In reality, they are all located on the device.

Computers that have the Mac OS pre-installed are usually configured with a single partition with the Mac OS Extended (HFS+) file system.

When installing on one of the listed computers, Mac OS X must reside within the first 8GB of the drive. There are two likely scenarios that would prevent the installation from continuing:

If your computer has a hard drive greater than 8GB, which is mounted as a single volume, the OS X installation will not be allowed. The only option in this case is to partition your drive.
If you have a large hard drive in your computer and it is split into partitions that exceed 8GB, none of the partitions will be available for installation. You must delete and re-create the first partition so that the first portion of it is less than 8GB.

Unfortunately, the Macintosh does not support partitioning without destroying the data on your drives. If your computer is one of the affected models and your drive requires partitioning, the only option is to back up your computer, repartition, and then continue with the installation. We'll look at the process of partitioning in the "Partitioning Your Drive" section later in this chapter. Assuming that issues with drive partitioning do not affect your machine, you can proceed directly to the Mac OS X installation guide.

Performing a Clean Installation

Although upgrading an existing 9.x installation is acceptable, it might not lead to the best possible system performance. Many users have found that Mac OS X's Classic environment is incompatible with various system extensions that they were using at the time of the upgrade. The process of finding the incompatible extensions while running Mac OS X is time-consuming and nonintuitive. Personally, I recommend starting from scratch with Mac OS X. Apple has done an admirable job of allowing OS X to install on top of the older OS; however, if a problem does occur, it might not be easy to track down.

Another consideration is drive partitioning. If you've decided to go with a clean install, you might want to think about partitioning your existing drive into separate volumes for Mac OS 9 and Mac OS X.

Partitioning Your Drive

Partitioning creates one or more logical volumes contained within the single hard disk. This process is often used to separate system-critical files from user files. Standard Unix implementations usually have multiple partitions for the operating system, user directories, applications, and application support files. Mac OS X breaks this tradition by using a single primary partition for all data.

For the time being, it's easier to follow the OS X all-in-one model than it is to fight it. Multiple partitions are visible under Mac OS X, but to use them with the base operating system as anything other than additional file storage, you'll need to work directly with the command line. Because Apple is pushing its auto-update application, making changes to the base configuration of the operating system by hand is not advisable.

Note

Users coming from more conventional Unix/Linux distributions will likely take issue with the Mac OS X partition setup. It is important to keep in mind that the system was designed from the perspective of a traditional Mac user.

Under earlier versions of Mac OS, all storage media is mounted in the same location and accessible to the user as independent volumes. Unix users are more accustomed to being able to mount storage media anywhere in their file system. For example, suppose that a user has a My Documents directory somewhere on her system and would like to dedicate an entire drive to that. On Mac OS, the drive would be forced to sit on the desktop, just like the main boot volume. Under Unix, the new drive could be mounted directly at the level of the My Documents folder. This becomes what is called a mount point. Although this is possible on Mac OS X, it is not easily accomplished with the included GUI tools.

So, if Apple isn't making drive partitioning a necessity, why bother doing it at all? There are a few reasons why a partitioned drive might be beneficial to your system:

Compatibility with existing Unix systems— Mac OS X supports both HFS+ and UFS (Unix File System). This allows it to easily interoperate with other Unix-based operating systems, including the original version of Mac OS X Server. Creating a UFS-based partition on a drive would allow the drive to be mounted and used under other operating systems, and then moved to Mac OS X. Very few operating systems other than Mac OS support the native file system type of HFS+.

What Is the Difference Between a Partition and a File System?

A partition is a logical division of the storage medium into subvolumes. A partition does not define the contents of the subvolume, just the position on the disk and amount of space consumed.

Before a partition can be used, it must have a file system installed. A file system defines the way data will be stored on a given partition. The terms partition and file system are intimately related, and can often be used interchangeably, but they operate at two different levels on the hard drive.

Separating critical resources— Although Mac OS X partitions are mounted as individual volumes, that doesn't prevent you from taking advantage of the separation of resources. Partitions are based on a single hard drive, but are independent of one another. For example, if you have three partitions on a single drive, unless there is an actual physical problem with the drive or a low-level error in the driver software, the contents of the three partitions cannot affect one another in any way.
Drive errors typically come in the form of file system corruption, rather than a true crash of the disk hardware. If you've ever been forced to boot from a CD after a system crash, only to see the message "This disk cannot be read, erase?" you've experienced file system corruption. By dividing critical data, you can lessen the risk of file corruption occurring to a given volume. A partition created solely for the purposes of storing documents is unlikely to be affected by a serious system crash. Although you might need to reinstall your operating system, your data will probably still be safe.

Unfortunately, even though partitions limit damage from everyday use, physical problems can still occur on a hard disk itself that might result in data loss across all partitions. Backup options are covered in Chapter 32, "Maintenance and Troubleshooting."
Disk fragmentation— Disk fragmentation is similar to file system corruption. For Mac users, disk fragmentation is a way of life. The Macintosh operating system makes it too easy to install, remove, and move files, while doing a poor job of allocating storage for these files. Over the course of time, disk accesses can slow significantly.
If you're using both Mac OS 9.x and OS X running from the same volume, your interactions when booted into 9.x can have the same detrimental effect on the file system. Keeping Mac OS 9.x and Mac OS X in separate partitions results in a cleaner environment that is less susceptible to fragmentation.

For the sample installation shown in this chapter, I will use one partition for Mac OS 9.x, and a second partition for Mac OS X.9.x.
Boot Options— By using separate partitions for Mac OS X and Mac OS 9, you can use the Open Firmware startup selection to choose the boot volume. This provides an excellent means of starting the computer if Mac OS X (or 9) fails.

Creating the Partitions

The first step in partitioning your drives is to choose the type of file system that will be installed on the partition.

As mentioned earlier, two types of file systems are supported within Mac OS X:

UFS—Unix File System
HFS+—Hierarchical File System Plus

The recommended file system for Mac OS X installations is HFS+. HFS+ has been the Macintosh file system since the late 1990s, and is compatible with your existing Mac drives. UFS, on the other hand, exists for compatibility in Unix environments. If you're using OS X on its own, or with other Macs, choose HFS+.

There is one very important difference between HFS+ and UFS that might cause nervous breakdowns for those used to working within a Unix environment: The Macintosh file system has been, and continues to be, case insensitive.

This means that a file named John.doc is identical to one named john.doc. Case insensitivity is one of the ease-of-use features of the Macintosh that does not translate well into the Unix environment. Programmers who have written scripts that use differences in case to differentiate between files will have to rework the applications to function in a case-insensitive environment.

The case issue can cause problems if a Mac OS X installation is required to provide complete compatibility with existing Unix software. If you're using OS X as a migration platform from Linux or another Unix system, you might want to consider using UFS rather than having to review all the code that is currently in place.

Caution

Amusingly enough, one of the first companies to be bitten by the case sensitivity issue is Apple. Although Mac OS X will install and operate correctly on the UFS file system, the AirPort wireless driver package makes the assumption that it is on a case-insensitive system. When it attempts to load components of the driver, it fails because the files could not be located. If you're using UFS as your installation partition type, you will not be able to use your wireless network.

You can read more about this almost-amusing bug in Apple's Tech Info Library (TIL) reference: http://til.info.apple.com/techinfo.nsf/artnum/n106252.

Apple's Tech Info Library is the source for updated information, problems, and solutions related to Mac OS X and other Apple products. Before calling technical support or turning to a user group, always check the TIL!

Assuming that you're going with the HFS+ file system, you'll need to choose the size and number of partitions to be created. In the original HFS implementation, file allocation block size was determined by dividing the total drive storage by 65,536. As drive space grew, storage efficiency plummeted. The HFS+ file system uses 4KB blocks no matter what the size of the containing partition. Because of this, partitioning is no longer necessary to maintain drive efficiency. Other than the reasons already discussed, your partition sizes are up to you.

What Is a File Allocation Block?

Instead of allowing every file to take advantage of every bit of available space, file systems allocate blocks of space that are used one at a time. The total amount of space that a file takes up must be a multiple of the block size, regardless of whether all the space is used.

In the original Mac OS HFS implementation, on a 1GB drive, a single file allocation block takes up 16KB (1024*1024/65536). This means that a file whose size is 1KB will actually consume 16KB on the drive. On HFS+ (the default file system of Mac OS X), the block size is 4KB, so the same 1KB file will take up only 4KB.

Extrapolate this to today's high-capacity hard drives, and you'll see that if HFS were used on an 80GB drive, a 1KB file would occupy more than 1MB of total drive space!

Running Drive Setup

When you're ready to partition your drive, boot your Macintosh from the 9.x CD that is included in your Mac OS X package. To boot from the CD, start the computer with the CD-ROM in the drive while holding down the C key. It is important that you use the Apple-supplied 9.x CD rather than an earlier version of the operating system. Version 1.8.1 of the HD Setup tool creates UFS partitions that are incompatible with Mac OS X.

On booting your Macintosh from Mac OS 9.x, start the Drive Setup application located in the Utilities folder. The program should show a list of the available hard drives, as shown in Figure 2.6. On a system with a single drive, there will be two entries: one for the CD that booted the system and one for the hard drive.

Figure 2.6 Choose the hard drive that you want to set up.

To begin the process of partitioning, choose the disk in the list that matches the drive you want to use for your Mac OS X installation. EIDE drives are listed under the type ATA, whereas SCSI disks are of the type SCSI. After making your selection, click the Initialize button.

Choosing a Partition Scheme

Drive Setup will warn you, as demonstrated by the dialog box in Figure 2.7, that all the data on your drive is about to be deleted.It will also give you the option to create a custom setup. This is where you can choose the partition scheme you'd like, or choose between the HFS+ and UFS file systems.

Figure 2.7 Click Custom Setup to create a new partition scheme.

The Custom Setup dialog box makes it easy to create multiple partitions on a drive. The left portion of the window shows a visual representation of the hard drive and the subvolumes (partitions) that have been created. A black border surrounds each partition. This border can be dragged to change the amount of space allocated to that partition.

To the right of the highlighted partition is displayed the name, type, and size (in megabytes) of the selected item. You can change these values to change the type and size of the partition. To create a partition scheme, choose the number of partitions that you want to use from the Partitioning Scheme pop-up menu located at the top of the dialog box. Figure 2.8 shows a dual partition schema with two Mac OS Extended (HFS+) partitions.

Figure 2.8 Create your partition scheme.

If you want to delete partitions, select them and press the Delete key on your keyboard, or choose a new schema from the pop-up menu and start again. By default, the partitions that you create will use the Mac OS Extended file system. Unless you plan to use UFS, no changes should need to be made to the partition type.

After choosing the partition layout, click the OK button to go back to the warning screen that cautions about all data being destroyed. If you're sure that there's nothing you want on the disk, click Initialize.

Drive Setup will take approximately 10 seconds per partition to initialize your new drive structure. After initialization is completed, the drives will be mounted on your Mac OS 9.x desktop.

You should take this opportunity to name the two drives. The first partition (named "untitled") will typically be the Mac OS X partition. Again, if you're using one of the older iMacs/G3s, the first partition might have to be the Mac OS X partition. The subsequent partitions will be named untitled2, untitled3, and so on. Assuming that you've created a two-partition configuration, the second partition can be named Mac OS 9.x. Although this isn't necessary for Mac OS X to be installed correctly, it will help you identify the appropriate drives to choose during your Mac OS X installation.

You're now ready to install Mac OS 9.x.

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