Help in setting RAID levels
Rick Cook
Setting RAID levels on a disk array is a deceptively simple job that can result is less-than-optimum performance. The job is simple because it's easy to set RAID levels, once you understand them. It's deceptively simple, because deciding which RAID level to use for storage should take careful analysis of the data being stored and how it is used. Some people avoid that requirement by simply picking a RAID level, such at 5 or 10, and using it for everything. This can cause sub optimal performance, and may even risk losing data if the level is really wrong for the job.
Several RAID products provide various degrees of help in choosing and setting RAID levels.
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Mylex Corporation, for example, offers a software module with its controllers that automates the process. The product, called EzAssist, will automatically set the RAID level on storage attached to a Mylex controller, or it will ask you a few questions about the use of the storage and set the RAID level accordingly. Alternatively, you can set the RAID level in the conventional manner.
Another aid to storage managers is the ability to add storage to a RAID array without having to reconfigure the LUN. Among others, Advanced Media Services offers the feature on Heritage RAID systems. With the Heritage systems, the administrator can add disk drives to an array configured at level 1, 3 or 5 without reconfiguring the system.
Hewlett Packard offers a more comprehensive approach with its SureStore Virtual Arrays 7400 and 7100. These arrays not only select the RAID level, but they can change it dynamically to meet the way the storage is being used. The systems do this by managing data down to the cluster level and by using a dynamic mapping system to allocate and de-allocate clusters of any RAID type.
Editor's note: Mention of specific products in this tip is not meant to indicate that these products are the only ones offering features similar to those mentioned. Further, mention of specific products does not imply endorsement of these products. Such mentions are for illustrative purposes only, and are not intended to be an exhaustive list of such products.
Rick Cook has been writing about mass storage since the days when the term meant an 80K floppy disk. The computers he learned on used ferrite cores and magnetic drums. For the last twenty years he has been a freelance writer specializing in storage and other computer issues.
This was first published in January 2002