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Storage Server 2003 add-ins may cause slowdown

Combining Windows Storage Server 2003 with a Windows NFS Server and software-based RAID may cause a major performance hit. The problem is caching. Here's a solution.

Call it subtraction by addition. If you combine Windows Storage Server 2003 with a Windows NFS Server and software-based RAID, you may wind up with a surprise: a major slowdown. Performance is likely to be noticeably worse than it was under the older Windows Powered NAS, and file transfers will be even slower than they are with an NFS Server running Windows Services for Unix.

The problem is caching -- specifically, the interaction between the Server for NFS software and Storage Server 2003 when the system performs writes. In Storage Server 2003, Server for NFS doesn't cache writes in the system cache; instead it writes the data directly to disk. This can have a serious impact on performance in RAID, especially RAID 5 (block level striping with parity), which performs several writes for each block written to the disk.

According to Microsoft, the solution is to use a disk controller with a battery-backed cache. Turning on the cache reduces the number of writes to the disks, thereby increasing performance. However, the cache should be protected against power failures, since the data in the cache will be lost in the event the controller loses power before the cache is flushed to disk. This will corrupt the files.

Microsoft discusses this situation in Knowledge Base article 894722.

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 20 years he has been a freelance writer specializing in issues related to storage and storage management.

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