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10
4.2.3
General performance characteristics
Minimum sector interleave
Data buffer to/from disc media (one 512-byte logical block)*
Minimum
Maximum
Fibre Channel Interface maximum instantaneous transfer rate
Logical block sizes
Default is 512-byte data blocks
Variable (180 to 736 bytes) in multiples of 4 bytes
Variable (768 to 4,096 bytes) in multiples of 32 bytes
Read/write consecutive sectors on a track
Overhead time for head switch in sequential mode
Overhead time for one track cylinder switch in sequential mode
Average rotational latency
*Assumes no errors and no relocated logical blocks.
4.3
Start/stop time
If the Motor Start option is disabled, the drive becomes ready within 30 seconds after DC power is applied. If a
recoverable error condition is detected during the start sequence, the drive executes a recovery procedure and
the time to become ready may exceed 30 seconds. During the start sequence, the drive responds to some
commands over the FC-AL interface. Stop time is less than 30 seconds (maximum) from removal of DC power.
If the Motor Start option is enabled, the internal controller accepts the commands listed in the Fibre Channel
Interface Manual less than 3 seconds after DC power has been applied. After the Motor Start command has
been received, the drive becomes ready for normal operations within 30 seconds (excluding the error recovery
procedure). The Motor Start command can also be used to command the drive to stop the spindle.
There is no power control switch on the drive.
4.4
Prefetch/multi-segmented cache control
The drive provides a prefetch/multi-segmented cache algorithm that in many cases can enhance system per-
formance. To select this feature the host sends the Mode Select command with the proper values in the appli-
cable bytes in page 08h. Default is prefetch and read cache enabled.
If the Prefetch feature is enabled, data in contiguous logical blocks on the disc immediately beyond that which
was requested by a Read command are retrieved and stored in the buffer for immediate transfer from the
buffer to the host on subsequent Read commands that request those logical blocks (this is true even if cache
operation is disabled). To enable Prefetch, use Mode Select page 08h, byte 12, bit 5 (Disable Read Ahead -
DRA bit). DRA bit = 0 enables prefetch.
Since data that is prefetched replaces data already in some buffer segments, the host can limit the amount of
prefetch data to optimize system performance. The Max Prefetch field (bytes 8 and 9) limits the amount of
prefetch. The drive does not use the Prefetch Ceiling field (bytes 10 and 11).
4.5
Cache operation
Refer to the Fibre Channel Interface Manual for more detail concerning the cache bits.
Note.
Of the 1,024 Kbytes physical buffer space in the drive, 967.5 Kbytes can be used as a cache. The cache can
be divided into logical segments from which data is read and to which data is written.
Cheetah 4LP FC Product Manual, Rev. A
ST34501FC
1 to 1
15.25 MBytes/sec
22.12 MBytes/sec
106.3 Mbytes/sec*
Yes
0.798 msec
<1.064 msec (typical)
2.99 msec
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