During a quarterly capacity review, you analyze Performance Monitor logs from a write-intensive SQL Server whose data files reside on an eight-disk RAID-10 set built with 15 000 RPM SAS drives. The manufacturer rates each drive at sustaining roughly 200 random write IOPS. Based on RAID-10 write characteristics, what is the nearest value you should record as the maximum sustained write IOPS this array can deliver before queuing and latency become a concern?
A RAID-10 array stripes mirror pairs. Every logical write operation must be written to both members of each mirror, so effective write throughput is one-half of the total spindle IOPS (write penalty = 2).
IOPS per spindle × number of spindles = 200 × 8 = 1600 theoretical writes/sec. Dividing by the penalty (2) gives about 800 sustained write IOPS. Values such as 1600 or 3200 ignore the RAID-10 write overhead, while 400 underestimates the capacity by applying the penalty twice.
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