C
ONSTELLATION
ES.1 SAS P
RODUCT
M
ANUAL
, R
EV
. G
10
4.2.3
General performance characteristics
Minimum sector interleave
1 to 1
Data buffer to/from disk media (one 512-byte logical block)*
95 to 212 MB/s
Sustained transfer rate
62 to 152 MB/s
SAS Interface maximum instantaneous transfer rate
600MB/s* per port
(dual port = 1200MB/s*)
Logical block sizes
512 (default), 520 or 528.
Read/write consecutive sectors on a track
Yes
Flaw reallocation performance impact (for flaws reallocated at format time using the spare sectors per sparing
zone reallocation scheme.)
Negligible
Average rotational latency
4.16ms
*Assumes no errors and no relocated logical blocks. Rate measured from the start of the first logical block transfer to or from the host.
4.3
S
TART
/
STOP TIME
The drive accepts the commands listed in the SAS Interface Manual less than 3 seconds after DC power has been applied.
If the drive receives a NOTIFY (ENABLE SPINUP) primitive through either port and has not received a START STOP UNIT command with
the START bit equal to 0, the drive becomes ready for normal operations within 30 seconds (excluding the error recovery procedure).
If the drive receives a START STOP UNIT command with the START bit equal to 0 before receiving a NOTIFY (ENABLE SPINUP)
primitive, the drive waits for a START STOP UNIT command with the START bit equal to 1. After receiving a START STOP UNIT command
with the START bit equal to 1, the drive waits for a NOTIFY (ENABLE SPINUP) primitive. After receiving a NOTIFY (ENABLE SPINUP)
primitive through either port, the drive becomes ready for normal operations within 30 seconds (excluding the error recovery procedure).
If the drive receives a START STOP UNIT command with the START bit and IMMED bit equal to 1 and does not receive a NOTIFY
(ENABLE SPINUP) primitive within 5 seconds, the drive fails the START STOP UNIT command.
The START STOP UNIT command may be used to command the drive to stop the spindle. Stop time is 20 seconds (maximum) from
removal of DC power. SCSI stop time is 20 seconds. There is no power control switch on the drive.
4.4
P
REFETCH
/
MULTI
-
SEGMENTED CACHE CONTROL
The drive provides a prefetch (read look-ahead) and multi-segmented cache control algorithms that in many cases can enhance system
performance. Cache refers to the drive buffer storage space when it is used in cache operations. To select this feature, the host sends the
Mode Select command with the proper values in the applicable bytes in page 08h. Prefetch and cache operations are independent
features from the standpoint that each is enabled and disabled independently using the Mode Select command; however, in actual
operation, the prefetch feature overlaps cache operation somewhat as described in sections 4.5.1 and 4.5.2.
All default cache and prefetch mode parameter values (Mode Page 08h) for standard OEM versions of this drive family are given in Table
10.
4.5
C
ACHE OPERATION
Note.
Refer to the
SAS Interface Manual
for more detail concerning the cache bits.
Of the 64MB physical buffer space in the drive, approximately 30,000 kbytes can be used as a cache. The buffer is divided into logical
segments from which data is read and to which data is written.
The drive keeps track of the logical block addresses of the data stored in each segment of the buffer. If the cache is enabled (see RCD bit
in the
SAS Interface Manual
), data requested by the host with a read command is retrieved from the buffer, if possible, before any disk
access is initiated. If cache operation is not enabled, the buffer is still used, but only as circular buffer segments during disk medium read
operations (disregarding Prefetch operation for the moment). That is, the drive does not check in the buffer segments for the requested
read data, but goes directly to the medium to retrieve it. The retrieved data merely passes through some buffer segment on the way to the
host. All data transfers to the host are in accordance with buffer-full ratio rules. See the explanation provided with the information about
Mode Page 02h (disconnect/reconnect control) in the
SAS Interface Manual
.
