The sheer size of many Exchange Server files -- the database, mainly, but also the log files -- can eat up a lot of disk space. Any hard drive that's over 75% to 80% capacity is going to be hard to defragment (especially if it's already badly fragmented), and will experience other performance degradations on top of that.
To alleviate the problem, some Exchange Server administrators have debated using NTFS's native file-compression system on some Exchange Server files to save hard drive space -- but this is generally not a good idea..
When people think of NTFS file compression (which allows files to be compressed and decompressed on the fly), they think of technologies like Stacker or Disk Doubler -- which were not terribly stable and caused at least as many problems as they solved.
Back when disk space was at a premium, these NTFS compression solutions were at least provisionally attractive. But now that disk space is so much cheaper, it makes more sense to simply buy the storage you need instead of wrestling with a software solution.
Granted, NTFS file compression is a lot more dependable now than the technologies that were available back in the days of DOS and 16-bit/32-bit Windows. Even so, I would still be reluctant to use it to compress live data on any production machine, especially data used by Exchange Server.
The main reason for not using NTFS file compression on Exchange Server is performance. There's a certain amount of overhead involved in compressing and decompressing data. If you multiply that overhead by the number of concurrent I/O requests made to such data, you have a recipe for an Exchange server that's going to take a performance hit -- no matter how many cores you have in it. The Exchange Server databases themselves (and the binaries) should never be compressed.
The only Exchange Server files that I would feel comfortable setting as NTFS-compressed would be Exchange Server log files -- not the transaction logs -- but logs generated by SMTP logging.
SMTP log files do compress very well -- 75% or better, since they're essentially plaintext. But if they're not really needed, they can simply be archived using a third-party archiving tool that yields better compression than NTFS on-disk compression; or you could just delete them entirely.
About the author: Serdar Yegulalp is editor of Windows Insight, a newsletter devoted to hints, tips, tricks, news and goodies for all flavors of Windows users.
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Related information from SearchExchange.com:
Expert Advice: Can I compress an Exchange 2000 database?
Tip: How to automatically purge Exchange-related logs
Tip: Increase Exchange Server disk performance with aligned partitions
Best Practices Guide: Optimize Exchange Server disk performance
Checklist: Top 10 Exchange Server performance worst practices
Learning Guide: Exchange Server performance tuning
Reference Center: Exchange Server database management tips
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