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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
Average
Maximum
Data buffer transfer rate to/from disc media (<1 track)*
Minimum
Average
Maximum
Fibre Channel Interface maximum instantaneous transfer rate
Logical block sizes
Default is 512-byte data blocks
Variable 512 to 4,096 bytes per sector in even number increments
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 31 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 31 seconds. During the start sequence, the drive responds to some
commands over the FC-AL interface. Stop time is less than 31 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 13 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 opera-
tion 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).
Barracuda 18FC Product Manual, Rev. B
ST118273FC
1 to 1
15.2 MBytes/sec
20.4 MBytes/sec
23.7 MBytes/sec
10.8 MBytes/sec
16.0 MBytes/sec
17.0 MBytes/sec
106 Mbytes/sec* per port
(dual port = 212 Mbytes/sec*)
Yes
1.2 msec
1.2 msec (typical)
4.17 msec
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