CompTIA A_ Certification All-In-One Exam Guide, Seventh Edition - Michael Meyers [196]
Most of the time, formatting is a slow, boring process. But sometimes the drive makes “bad sounds” and you start seeing errors like the one shown in Figure 12-67 at the top of the screen.
An allocation unit is FORMAT’s term for a cluster. The drive has run across a bad cluster and is trying to fix it. For years, I’ve told techs that seeing this error a few (610) times doesn’t mean anything; every drive comes with a few bad spots. This is no longer true. Modern drives actually hide a significant number of extra sectors that they use to replace bad sectors automatically. If a new drive gets a lot of “Trying to recover lost allocation unit” errors, you can bet that the drive is dying and needs to be replaced. Get the hard drive maker’s diagnostic to be sure. Bad clusters are reported by S.M.A.R.T.
Figure 12-67 The “Trying to recover lost allocation unit” error
Mental Reinstallation Focus on the fact that all of these errors share a common thread—you just installed a drive! Installation errors don’t show up on a system that has been running correctly for three weeks; they show up the moment you try to do something with the drive you just installed. If a newly installed drive fails to work, do a “mental reinstallation.” Does the drive show up in the CMOS autodetect? No? Then recheck the cables, master/slave settings, and power. If it does show up, did you remember to partition and format the drive? Did it need to be set to active? These are commonsense questions that come to mind as you march through your mental reinstallation. Even if you’ve installed thousands of drives over the years, you’ll be amazed at how often you do things such as forget to plug in power to a drive, forget CMOS, or install a cable backward. Do the mental reinstallation—it really works!
Data Corruption
All hard drives occasionally get corrupted data in individual sectors. Power surges, accidental shutdowns, corrupted installation media, and viruses, along with hundreds of other problems, can cause this corruption. In most cases, this type of error shows up while Windows is running. Figure 12-68 shows a classic example.
Figure 12-68 A corrupted data error
You may also see Windows error messages saying one of the following:
“The following file is missing or corrupt”
“The download location information is damaged”
“Unable to load file”
If core boot files become corrupted, you may see text errors at boot, such as the following:
“Cannot find COMMAND.COM”
“Error loading operating system”
“Invalid BOOT.INI”
“NTLDR is missing or corrupt”
On older programs, you may see a command prompt open with errors such as this one:
Sector not found reading drive C: Abort, Retry, Fail?
The first fix for any of these problems is to run the Error-checking utility. Error-checking will go through and mark bad clusters and hopefully move your data to a good cluster.
Windows 2000/XP Extract/Expand If Error-checking fails to move a critically important file—such as a file Windows needs so it can load—on pre-Vista systems you can always resort to the command line and try to extract the file from the Windows cabinet files. Most Windows programs store all files in a compressed format called CAB (which is short for cabinet file). One CAB file contains many files, and most installation discs have lots of CAB files (see Figure 12-69).
Figure 12-69 CAB files
To replace a single corrupt file this way, you need to know two things: the location of the CAB file that contains the file you need, and how to get the file out so you can copy it back to its original spot. Microsoft supplies the EXPAND program to enable you to get a new copy of the missing file from the CAB files on the installation CD-ROM. Also notice how they are numbered—that’s the secret to understanding these programs.
In most cases, all of the CAB files for a program are piled into some folder, as shown in Figure 12-69. Let