Ask the Expert

Is disk defragmentation really necessary on Compaq Smart Raid systems?

I read your article on disk fragmentation in which you indicated that defragmentation is still needed on RAID disks and SAN.

I am supporting a number of Compaq ProLiant servers which are all running on Smart controllers, i.e. hardware RAID. In an unofficial conversation with a Compaq support expert, he indicated that disk defragmentation was not necessary on Compaq SMART RAID systems. What are your comments on this?

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Fragmentation is a fact - there is no doubt about it. No OS is capable of keeping all files continous. This is due to several reasons:

Files increase and decrease in size, or will be deleted and recreated. This process is not predictable. The OS tries to keep existing pieces of files in their place and allocates new clusters when needed. These can be at a completely different location, thus leading to a fragmentation of the file. Imagine you are hosting a file server where dozens or even hundreds of users are working concurrently. This will definitely lead to a fragmentation.

Also, the level of free space fragmentation can increase significantly over time as files will be deleted and created. This will undoubtedly decrease the performance of the file system. Defragmentation is the only way to regain performance and keep it at a peak level.

Remember the days when Microsoft told us that NTFS does not fragment? Nowadays, they are packing Windows with a light defragger to give you the hint that this is mission critical for the OS!

Many hardware manufacturers do not recognize the benefits of regular defragmentation. PCs today are much faster than in years past, but the percentage of the performance decrease stays the same. If you are running servers, you will see the difference. Also, keep in mind that applications today access files more frequently than their predecessors. Even on a workstation you will notice a speed increase after a defragmentation.

This was first published in May 2002

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