Should administrators use hard disk compression?

Should admins use hard disk compression? There's no right or wrong answer. Weigh the pros and cons of hard disk compression and learn when compressing the hard drive can be harmful.

Brien M. Posey
Brien M. Posey
I was recently having dinner with a friend at a tech conference and the subject of disk compression came up. My friend said he uses disk compression as a way of improving a machine's performance. I was somewhat surprised because I had never used disk compression for that purpose.

While hard disk compression removes redundancy from files as they are written to disk, which helps conserve disk space, there is tradeoff: When files are read from disk, they must be decompressed on the fly. The decompression process consumes CPU resources that would not otherwise be used if the file is not compressed. Because of this, I always assumed that a machine would perform better if disk space was left decompressed.

So when I learned that my friend uses disk compression to improve system performance, I was a bit taken back. I know my friend is no idiot, so there had to be a reason for him to suggest that compressing a hard disk could improve performance.

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Curious, I asked him to explain his reasoning. Turns out, he found that the hard disk was the slowest component in the entire system and that one way to speed up the system was to minimize the amount of data that must be written to or read from a disk. Compression reduces the file size stored on disk, thereby speeding up disk I/O.

When I asked him about the decompression process, he explained that it was necessary, but that it occurs after the file has already been read from the disk. Since memory is a faster medium than the hard disk, the decompression process happens very quickly.

So the question remains: Should you compress your hard drive or not?

There's no right answer because no two people use their computers exactly the same way. In my opinion, determining whether it's prudent to compress the drive will depend on the types of data reside on a hard drive and the way the data is used.

For example, suppose you have a drive that contains .jpg images. It wouldn't make sense to compress the hard drive, because .jpgs are already compressed, which means disk compression won't save you much space. And in some cases, compressing a file that's already in a compressed format can actually cause the file to take up more space.

On the other hand, you might want to consider compressing a hard drive if it is used to store a lot of old files that are seldom accessed. In that scenario, compressing the drive could save space, and the performance impact would not be a factor because the files are rarely accessed.

When it comes to compressing files and whether doing so provides a quicker read, I believe it would work, but only under certain circumstances. For instance, if you have large files that require a read fairly often, then compression might actually improve performance. In the case of smaller files, though, I think that compression may actually hurt performance.

Even in the case of large files, however, admins first need to consider whether the machine has the CPU resources available that would allow efficient decompression. If a machine is already low on memory and CPU resources, then compression will hurt performance. In most cases, though, I think that you are probably better off not compressing a volume.

Brien M. Posey, MCSE, has received Microsoft's Most Valuable Professional Award four times for his work with Windows Server, IIS and Exchange Server. He has served as CIO for a nationwide chain of hospitals and healthcare facilities and was once a network administrator for Fort Knox. You can visit his website at www.brienposey.com.


This was first published in April 2009

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