Mac OS X Leopard - ARCAism

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CHAPTER 6 COMMON LEOPARD MAINTENANCE
NOTE There are two primary things that can go wrong on a disk: there’s physical damage,
which is when the disk mechanism fails and possibly crashes, and there’s file system damage,
which is when the data on your disk gets mixed up or damaged. Tools like Disk Utility can often
detect and repair file system damage before it causes data loss. Physical damage to the disk is
more permanent, and often irreparable (although in some cases the data can be recovered by
special hardware and/or software).
NOTE The term disk crash refers to the event when the arms that pass over the disk surface
to read the data fall and literally crash into the disk’s surface, causing irreparable damage. This
used to happen with older disk mechanisms that would rely on the air force of the spinning
disk to keep the arms up, so if the disks quit spinning suddenly before the arms could move
back off the disk’s surface (e.g., in a power failure), the arms would fall. Disk crashes like this
don’t happen with today’s hard drives, but mechanical issues still arise, and disks do get old
and eventually wear out (usually after years of service, though).
Disk Utility divides its abilities into five areas: First Aid, Erase, RAID, Restore, and Partition.
First Aid provides a couple of general maintenance tools that can help identify and repair
both file system damage and issues in which the system’s file permissions become altered. The
Erase tab provides the necessary tools to partition and format a disk using various supported file
systems. The RAID tab allows you configure multiple disks to behave as one in various ways.
The Restore tab lets you restore a disk image onto a disk. We’ll cover each of these in the following
sections. The fifth area is Partition; it appears if you select the entire disk, rather than just
a volume in the list of devices on the left. The Partition tab allows you to split a single disk into
multiple volumes.
NOTE A disk is a physical device, whereas a volume is a file system written to a disk. The physical
space on a disk can be divided up into different volumes (or even left as empty space).
These divisions are referred to as disk partitions.
First Aid
The First Aid tab (Figure 6-1) allows you to run a few tasks to help identify and fix certain problems
with your disk’s file system. If you seem to be having issues with your disk or notice
anything unusual about how it’s running or storing data, this is the first place to go to try to
solve the problem.
In the lower-right-hand corner are two buttons: Verify Disk and Repair Disk. Clicking
Repair Disk will scan the disk to identify and repair many common file system errors. Although
most of the errors it may find are in themselves minor, they can often cause bigger issues down
the road. One gotcha here is that you can’t repair the boot volume—you can, however, click the
Verify Disk button to see if there are any problems with it, and if so, you can utilize the Repair
Disk function from the Disk Utility application included with your Leopard DVD (just boot
from your install DVD and run Disk Utility from there—don’t, however, start a new install
unless things are really hopeless). On occasion, the Repair utility will come across an issue it cannot
repair. At this point, you have two primary options (well, three if you are the type of person
who can just ignore a problem until it’s too late). Before you decide what you want to do, you
should first make backup copies of everything you value on your hard drive. Even if you already
have a copy, make another one (I have personally had a primary disk and a backup disk fail
simultaneously, and it was not a happy moment. Luckily I had another backup and only lost
about a month of work; now I use a mirrored RAID for my backup). Once that’s done, you can
do either of the following: