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[ The PC Guide | Systems and Components Reference Guide | Hard Disk Drives | Hard Disk Logical Structures and File Systems | Disk Compression ]

Compatibility and Reliability Issues in Volume Compression

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 $10 per gigabyte and prices falling fast, there is much less of a need to "stretch" the hard disk using compression. Another reason is related to 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, and these are few and far between.

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 most part.

I will state that I have used compression, from DoubleSpace to DriveSpace to DriveSpace 3, on several of my PCs for many years, and I have set up or maintained several dozen PCs that have used one version or another. In all of that time, 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. One of my PCs 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).

Next: New Technology File System (NTFS)


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