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21020690 B 6500 Disk Array User’s Guide
Chapter 3 Display/Operation Panel
Page 3 - 16 ARRAY INFORMATION
CAPACITY
Displays the logical block number of the last data block in the array. A value
followed by indicates a decimal number; a value followed by indicates a
hex number.
To calculate the capacity of the array, add one to the number displayed. For
example, a display with in an array formatted with 512 as the
sector size indicates that the array's capacity is 4,207,837 blocks of 512 bytes
each.
INITIATOR
INFO
A SCSI-2 bus can have up to 16 devices attached to it, with some devices acting
as initiators of SCSI commands, and some acting as targets. The array is always
a target.
The SCSI protocol allows targets and initiators to negotiate the width of the
bus to be used when transferring data, the transfer rate, and also whether the
transfer will be synchronous or asynchronous. This information is stored by the
array for each initiator on the SCSI bus under Array Information.
P is the Transfer Period
O is the Synchronous Offset
W indicates that a wide 16-bit bus will be used
N indicates that a narrow 8-bit bus will be used
To determine the Transfer Rate from the Transfer Period:
1. Translate the hexadecimal Transfer Period into decimal. For example,
19H equals decimal 25.
2. Multiply the decimal value by 4 to get the Transfer Period in
nanoseconds (25 x 4 = 100).
3. Take the reciprocal of this value to get the Transfer Rate in Megahertz
(1/100-
9
= 10 Megahertz).
4. Multiply by the bus width (1 or 2 bytes) to get the bus burst transfer
rate, e.g., 10 MHz x 2 bytes wide = 20MB/second.
Note Because the 6510 employs Wide Ultra SCSI technology, the SCSI
specification requires a slight variation to the computations above.
Wide Ultra SCSI technology is designated as 0CH or decimal 12,
when in fact it is slightly longer at 12.5. When the designated
period is multiplied by 4 to get the Transfer Period in nanoseconds,
the result is 48. In reality it is 50, which is the value whose
reciprocal 1/50 nanoseconds equals 20 Megahertz (20MB/
second).