User`s guide

3-47
Storage Manager
Command Statistics
Device I/O Statistics
The total number of sectors written to disk by the controller is
described by the formula:
Write – Backs + Write – Throughs = Total Sectors
However, in RAID 1 arrays
Write – Backs + Write – Throughs = 2 ∗ Total Sectors
This is because each sector written from the host results in a write
to each mirrored disk. In a RAID 5, each write from the host can
generate up to two disk reads and two disk writes. Because the
controller has cache memory, the reported number of sectors read
from or written to disk may be less than this value.
Total
Commands
The total number of commands received from the
host computer. This includes Read and Write
commands and other commands that may not
involve device I/O.
Misaligned
Transfers
The number of commands that required data to be
transferred starting at a RAM address location that
was not an even byte value.
SCSI Bus
Resets
The total number of SCSI bus resets that have been
issued by the controller. A large number of resets
can indicate a problem with the SCSI bus or an
attached device.
Combined RAID SW-UG.book Page 47 Monday, September 9, 2002 1:25 PM