Windows Vista Security: Praxisorientierte Sicherheit für Profis

Using Compression and Encryption

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With disks that have striped and spanned volumes, the drive status might show as

Failed, Online (Errors), or Unreadable. In many cases, you can resolve these prob-

lems using the same techniques as with simple volumes. Right-click the volume and

select Reactivate Disk. If this doesn’t work, click Rescan Disks on the Action menu.

You might also see the Missing or Offline status if drives have been disconnected or

powered off. In this case, you can try to reactivate or rescan, but this probably won’t

work. To resolve the problem, you may need to check the disk to ensure that it is

connected and that its power supply is connected. If you can’t fix the problem, you’ll

need to replace the disk. Shut down your computer before you try to examine your

computer’s hardware.

Using Compression and Encryption

When you format volumes with NTFS, you can use compression to reduce the disk

space used or encryption to add an extra layer of protection to your data. Because

these two options are mutually exclusive, a file or folder can be either compressed or

encrypted, not both. While you can compress or encrypt entire drives, you can also

compress or encrypt individual files and folders.

In Windows Explorer, compressed or encrypted NTFS files and fold-

ers are shown in color by default. Compressed files and folders are

shown in blue. Encrypted files and folders are shown in green.

Compressing Drives

When you format a volume with NTFS, Windows Vista allows you to turn on com-

pression for the entire disk. With compression enabled, any files created on or

moved to the disk are compressed automatically. When you open files or access fold-

ers, Windows Vista expands the files or folders for viewing as well. This behind-the-

scenes compression and expansion makes NTFS compression completely transpar-

ent, but it does use some of your computer’s processing power. With that said,

there’s an enormous benefit: you can store much more information on a compressed

drive.

You cannot compress encrypted data. If you try to do so, Windows

Vista automatically decrypts the data and then compresses it. Like-

wise, if you try to encrypt compressed data, Windows Vista expands

the data and then encrypts it.

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Chapter 19: Managing Disks and Drives

Compressing a drive

You can compress a drive and all its data by completing these steps:

1. In Windows Explorer or Disk Management, right-click the drive that you want

to compress and then select Properties.

2. On the General tab, select “Compress drive to save disk space” and then click

OK.

3. In the Confirm Attribute Changes dialog box, shown in Figure 19-15, specify

whether you want to compress only the top-level folder of the drive or the entire

drive:

• To compress only the drive’s top-level folder, select “Apply changes to drive...

only.”

• To compress the drive’s top-level folder, subfolders, and files, select “Apply

changes to drive ..., subfolders and files.”

4. Click OK.

Any files or folders you create on a compressed drive are compressed automatically.

Expanding a drive to remove compression

If you later decide that you no longer want to compress a drive, you can remove

compression from the drive. However, before you do this, you should ensure that the

drive has adequate free space to accommodate the expanded files. Typically, you’ll

need at least 50 percent more free space on the disk to expand its contents success-

fully. If a compressed disk currently uses 40 GB of space, this means you’d probably

need about 20 GB of free space to expand the disk successfully.

Figure 19-15. Confirming the compression options