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RAID-5 has some performance trade-off issues.
The perfomance of RAID-5 degrades as the ratio of writes to reads increases.
The reason why this is true is because when a data block that is written to
a RAID-5
volume, the XOR data block for that "cylinder" also need to be be updated.
This results is a corresponding additional write operation for the XOR data.
So when you have many read operation relative to the number of data write operations, there is minimal overhead from the RAID-5 volume. It would be a BAD idea to place the archive logfiles on a RAID-5 volume.
HTH & YMMV!