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Why to Do It:

Directory Damage

Amid all the bad news about things that can go wrong with your Mac, here is one piece of very good news: some of the most serious of Mac problems (such as an inability to start up your Mac) are often quickly and easily solved by a repair utility. This is because many of these problems can be traced to a damaged Directory, and these utilities can often fix the damage quickly. Here are the details:

The Directory The Directory area of a disk, as detailed in Chapter 8, is a collection of invisible data that contains the essential information that the Macintosh needs to access the disk and the files on it. Each area of the Directory has its own (often esoteric) name, such as extent BTree or catalog hierarchy.

The Directory maintains a continually updated catalog of the names, sizes, and locations of all files and folders on a disk. It is essentially a database. One very important function of the Directory is to keep track of the number of fragments of each file (see Fix-It #7) and where each fragment is located. For example, if a file is stored on a disk in fragments, the Directory contains the information needed to link all the fragments together when you launch the file. Without this information, fragmented files on the disk are unusable. Because almost all files on your disk are likely to be fragmented if you have not optimized recently, this can spell serious trouble.

The Directory (together with related "hidden" areas of the disk) also contains the critical information necessary for the Macintosh to recognize whether the disk is a Macintosh-formatted disk as well as whether it is a startup disk. Even a small amount of damage to the Directory can render an entire disk virtually inaccessible.

If anything is ever incorrectly updated, the Directory is considered damaged. Because the Directory is continually modified as you change the contents of your disk, and because most disk damage occurs when a file is modified, it is common for the Directory to become corrupted. Minor problems may cause symptoms so subtle that you do not notice them—at least not at first. This is why, in Chapter 2, I recommended using Disk First Aid as a preventative measure even if nothing seems wrong. You should eliminate even the most minor Directory problems as soon as you discover them, because minor problems tend to get more serious if left unfixed. Serious Directory problems can render the files on a disk inaccessible—you may not even be able to mount the disk.

Fortunately, if Directory damage occurs, there is still a very good chance that your disk, or at least most of the data on it, can be saved, because the remaining areas of the disk, where the documents and applications actually reside, may still be unharmed. The files contained on the disk are often all usable, if only they can be accessed. Working with a disk with a damaged Directory is a bit like trying to use a library without a catalog. The books are all fine, but there may be little hope of finding the ones you want.

Repairing the Directory Apple builds in sufficient redundancy to the structure of a disk so that even if a disk's Directory gets corrupted, a good repair utility can scan the undamaged portions of a disk, determine where the Directory errors are, and fix them. If this works, it is the ideal solution. It is almost like magic. An apparently dead disk can be restored to full working order in a matter of minutes, with no loss of data.

Disk First Aid Apple makes an excellent disk repair utility. It is called Disk First Aid and it is included free with every copy of the Mac OS. You will find it in the Utilities folder on the Mac OS CD. It will also be installed on your hard drive (in a Utilities folder) when you install the Mac OS. A copy was probably already there when you first booted your Mac. Finally, at least as of this writing, the Mac OS CD includes a Disk Tools image file that can be used to create a bootable floppy disk that contains Disk First Aid. It's called the Disk Tools disk. This is important because it may be necessary to start up from another disk, such as the Disk Tools disk, before you can repair your startup drive. Of course, in most cases, you can startup instead from the Mac OS CD itself, but for those Macs that still have floppy drives, the Disk Tools disk can sometimes be more convenient.

In general, I would use this first, before trying any other utility. I recommend it because, assuming you have the latest version of the utility, it may contain special fixes known only to Apple that will fix your problem where other utilities might not. However at least as often Disk First Aid will fail where other competitors might succeed. If Disk First Aid fails to solve the problem, simply move on to the next utility.

Beyond Disk First Aid There are currently three other popular disk repair utilities on the market. The first two are Norton Utilities for the Macintosh (especially the Norton Disk Doctor module) and TechTool Pro. Both do many more things beyond disk repair. For example, they may have the ability to check for media damage, recover files, unerase files, and/or optimize disks. We cover such matters in other Fix-Its (especially #11). Here we focus just on disk Directory repairs. The third utility in this category is DiskWarrior. As with Disk First Aid, all DiskWarrior does is Directory repair. However, DiskWarrior does it in a different way, completely replacing the Directory rather than trying to repair the existing one (the latest versions of TechTool Pro offer a similar option).

For the examples used in this Fix-It, I will use mainly Disk First Aid and Norton Disk Doctor. A "takenote" with more information on the other repair utilities is included near the end of this Fix-It.

What all of these utilities do is check for possible damage to a disk's Directory. They can then repair many, although not all, of the problems that they find. For preventative maintenance, run one or more of these utilities about once a month. If you have suspected Directory problems, immediately run the utility (or directory-checking module of the utility).

There are other causes of some of these symptoms, besides a damaged Directory (see the list at the end of this Fix-It). But if Directory damage does turn out to be the cause, and the damage is so severe that none of these utilities can repair it, usually your only remaining options are to reformat the disk or (for a removable media disk) discard it.



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