There are several reasons why compression isn't nearly as popular now as it was in the
past. One is simply the lack of necessity; with fast hard disks now less than $100 per
gigabyte and prices falling fast, there is much less of a need to "stretch" the
hard disk using compression. Another is concerns over performance. But probably the
biggest one is concerns over the reliability and safety of disk compression.
Some of these concerns are valid, but in my opinion most have been overblown. Mark
Twain said that a lie could make it half way around the world while the truth was still
putting on its shoes. Truly a wise man, he foresaw the creation of USEnet by a full century 
. Replace
"lie" with "bad news" and "truth" with "good news"
and you have the situation in a nutshell. Whoops, I digress. Must have spent too much time
writing this hard disk chapter. At any rate, there are some valid concerns regarding
compression which are worth looking at, if only to give them some perspective.
First, regarding compatibility, in my experience you will find very few problems. In
fact, the biggest problems with programs running on compressed disks have to do either
with conventional memory difficulties due to the compression driver, or reduced
performance due to decompression overhead, which can affect some software that needs high
performance. Virtually all regular programs see a compressed volume as just another disk,
and all modern utilities (written in the last few years anyway) will handle compressed
volumes just fine. Most software that is not meant for running on compressed disks will
tell you this in their instructions.
Some software will not work properly on a compressed volume because it cannot tolerate
the potential delay in decompressing the data. This delay can vary depending on how the
files are compressed and other factors. Some programs need real-time data streaming from
the hard disk without interruption. A CD-R recording utility would be a good example. This
sort of application (well, its data anyway) should be placed on an uncompressed volume.
There is a greater chance of a catastrophic data loss when using compressed volumes
than uncompressed volumes. The reason is that there is an extra layer of software
interpretation, and an extra layer of disk structures that can potentially become damaged.
Your entire compressed volume is stored in a single real file, the CVF, and if that file
should become damaged or accidentally deleted, you could lose some or all of the files on
the compressed volume. In practice, the use of compression today is quite safe. There were
in fact some problems with reliability associated with early implementations of the
technology, but these have been ironed out quite well for the mostpart.
I will state that I have used compression, from DoubleSpace to DriveSpace to DriveSpace
3, on all of my PCs for over 5 years, and I have set up or maintained several dozen PCs
that have used one version or another, and I have never had any problems relating to the
use of compression. That said, I recognize the increased possibility of data errors
resulting from compression, which is why I follow these general guidelines in how I use
it:
- Never Compress the Boot Drive: I do not set up PCs that have the C: drive
compressed. All of the sensitive disk structures and the operating system are on this
drive, and I think it prudent to leave these uncompressed. This also allows the system to
be bootable without the compression driver, if this ever becomes necessary, and also makes
it easier to deal with virus problems, should they arise.
- Compress Applications, Not Data: I generally use compression for items that can
be easily recreated in the event of loss, such as installed programs and especially games.
I don't generally compress data partitions. My PC at home has the games partition
compressed. (I use an uncompressed partition for games requiring faster performance.)
- Scan For Problems Regularly: The same utilities that are used to scan for trouble
on regular hard disks can be used to great effect on compressed drives, and should be run regularly to minimize long-term problems.
- Back Up Regularly: I harp on this a lot, and with good reason. In my opinion you
have little to fear from compression overall. If you back up your hard disk every week and
keep your sensitive data off your compressed partitions, you have basically nothing to
fear from it.
I believe that if used intelligently, compression is safe and has value, under the
correct circumstances. Of course, with hard disk sizes getting into the gargantuan range
and prices continuing to drop, I expect that compression will soon be a thing of the past
(but may become more popular in older PCs with small disks, as these strain with
trying to upgrade to newer and larger software).
Note: Windows NT is not
compatible with traditional compressed volumes. Of course, Windows NT provides far
superior file-based compression when you are using its advanced NTFS file system.
Next: Return To Hard Disk Drives Reference Guide
