Seagate ST300MM0026 Savvio 10K.1 SAS Product Manual - Page 20

14

Savvio SAS Product Manual, Rev. D

2.

When a requested logical block is reached that is not in any cache segment, the drive fetches it and any

remaining requested logical block addresses from the disc and puts them in a segment of the cache. The

drive transfers the remaining requested logical blocks from the cache to the host in accordance with the

Mode Select Disconnect/Reconnect parameters, page 02h.

3.

If the prefetch feature is enabled, refer to section 4.5.2 for operation from this point.

Case B

—A Read command requests data, and the first logical block is not in any segment of the cache:

1.

The drive fetches the requested logical blocks from the disc and transfers them into a segment, and then

from there to the host in accordance with the Mode Select Disconnect/Reconnect parameters, page 02h.

2.

If the prefetch feature is enabled, refer to section 4.5.2 for operation from this point.

During a prefetch, the drive crosses a cylinder boundary to fetch data only if the Discontinuity (DISC) bit is set

to 1 in bit 4 of byte 2 of the Mode Select parameters page 08h. Default is zero for bit 4.

Each cache segment is actually a self-contained circular buffer whose length is an integer number of logical

blocks. The wrap-around capability of the individual segments greatly enhances the cache’s overall perfor-

mance, allowing a wide range of user-selectable configurations. The drive supports operation of any integer

number of segments from 1 to 16. Divide the 6,900 Kbytes in the buffer by the number of segments to get the

segment size. Default is 3 segments.

Note.

The size of each segment is not reported by Mode Sense command page 08h, bytes 14 and 15.

The value 0XFFFF is always reported regardless of the actual size of the segment. Sending a size

specification using the Mode Select command (bytes 14 and 15) does not set up a new segment

size. If the STRICT bit in Mode page 00h (byte 2, bit 1) is set to one, the drive responds as it does

for any attempt to change an unchangeable parameter.

4.5.1

Caching write data

Write caching is a write operation by the drive that makes use of a drive buffer storage area where the data to

be written to the medium is stored while the drive performs the Write command.

If read caching is enabled (RCD=0), then data written to the medium is retained in the cache to be made avail-

able for future read cache hits. The same buffer space and segmentation is used as set up for read functions.

The buffer segmentation scheme is set up or changed independently, having nothing to do with the state of

RCD. When a write command is issued, if RCD=0, the cache is first checked to see if any logical blocks that

are to be written are already stored in the cache from a previous read or write command. If there are, the

respective cache segments are cleared. The new data is cached for subsequent Read commands.

If the number of write data logical blocks exceed the size of the segment being written into, when the end of the

segment is reached, the data is written into the beginning of the same cache segment, overwriting the data that

was written there at the beginning of the operation; however, the drive does not overwrite data that has not yet

been written to the medium.

If write caching is enabled (WCE=1), then the drive may return Good status on a write command after the data

has been transferred into the cache, but before the data has been written to the medium. If an error occurs

while writing the data to the medium, and Good status has already been returned, a deferred error will be gen-

erated.

The Synchronize Cache command may be used to force the drive to write all cached write data to the medium.

Upon completion of a Synchronize Cache command, all data received from previous write commands will have

been written to the medium.

Table 19 shows the mode default settings for the drive.

Section	Page
1.0 Scope	7
2.0 Applicable standards and reference documentation	9
2.1 Standards	9
2.1.1 Electromagnetic compatibility	9
2.1.1.1 Electromagnetic susceptibility	9
2.1.2 Electromagnetic compliance	10
2.2 Reference documents	11
3.0 General description	13
3.1 Standard features	14
3.2 Media description	14
3.3 Performance	14
3.4 Reliability	15
3.5 Formatted capacities	15
3.6 Programmable drive capacity	15
3.7 Factory-installed accessories	15
3.8 Factory-installed options	16
3.9 User-installed accessories	16
4.0 Performance characteristics	17
4.1 Internal drive characteristics	17
4.2 Seek performance characteristics	17
4.2.1 Access time	17
4.2.2 Format command execution time for 512-byte sectors (minutes)	18
4.2.3 General performance characteristics	18
4.3 Start/stop time	19
4.4 Prefetch/multi-segmented cache control	19
4.5 Cache operation	19
4.5.1 Caching write data	20
4.5.2 Prefetch operation	21
4.5.3 Optimizing cache performance for desktop and server applications	21
5.0 Reliability specifications	23
5.1 Error rates	23
5.1.1 Recoverable Errors	23
5.1.2 Unrecoverable Errors	23
5.1.3 Seek errors	24
5.1.4 Interface errors	24
5.2 Reliability and service	24
5.2.1 Mean time between failure	24
5.2.2 Preventive maintenance	24
5.2.3 Hot plugging the drive	25
5.2.4 S.M.A.R.T.	25
5.2.5 Thermal monitor	26
5.2.6 Drive Self Test (DST)	27
5.2.6.1 DST failure definition	27
5.2.6.2 Implementation	27
5.2.6.2.1 State of the drive prior to testing	28
5.2.6.2.2 Invoking DST	28
5.2.6.2.3 Short and extended tests	28
5.2.6.2.4 Log page entries	29
5.2.6.2.5 Abort	29
5.2.7 Product warranty	29
6.0 Physical/electrical specifications	31
6.1 AC power requirements	31
6.2 DC power requirements	31
6.2.1 Conducted noise immunity	33
6.2.2 Power sequencing	33
6.2.3 Current profiles	33
6.3 Power dissipation	36
6.4 Environmental limits	38
6.4.1 Temperature	38
6.4.2 Relative humidity	38
6.4.3 Effective altitude (sea level)	39
6.4.4 Shock and vibration	39
6.4.4.1 Shock	39
6.4.4.2 Vibration	41
6.4.5 Air cleanliness	41
6.4.6 Corrosive environment	41
6.4.7 Acoustics	42
6.4.8 Electromagnetic susceptibility	42
6.5 Mechanical specifications	43
7.0 Defect and error management	45
7.1 Drive internal defects/errors	45
7.2 Drive error recovery procedures	45
7.3 SAS system errors	46
8.0 Installation	47
8.1 Drive orientation	47
8.2 Cooling	48
8.3 Drive mounting	49
8.4 Grounding	49
9.0 Interface requirements	51
9.1 SAS features	51
9.1.1 task management functions	51
9.1.2 task management responses	51
9.2 Dual port support	52
9.3 SCSI commands supported	53
9.3.1 Inquiry data	57
9.3.2 Mode Sense data	57
9.4 Miscellaneous operating features and conditions	61
9.4.1 SAS physical interface	62
9.4.2 Physical characteristics	65
9.4.3 Connector requirements	65
9.4.4 Electrical description	65
9.4.5 Pin descriptions	65
9.4.6 SAS transmitters and receivers	66
9.4.7 Power	67
9.5 Signal characteristics	67
9.5.1 Ready LED Out	67
9.5.2 Differential signals	67
9.5.2.1 Eye masks	68
9.5.2.1.1 Eye masks overview	68
9.5.2.1.2 Receive eye mask	68
9.5.2.1.3 Jitter tolerance masks	69
9.5.2.2 Transmitter signal characteristics	71
9.5.2.3 Receiver signal characteristics	72
9.5.2.3.1 Jitter	72
9.5.2.3.2 Receiver jitter tolerance	73
9.5.2.3.3 Compliant jitter test pattern (CJTPAT)	73
9.5.2.3.4 Impedance specifications	73
9.5.2.4 Electrical TxRx connections	74
9.5.2.4.1 Transmitter characteristics	74
9.5.2.5 Receiver characteristics	77
10.0 Seagate Technology support services	79
Numerics	81
A	81
B	81
C	81
D	81
E	81
F	82
G	82
H	82
I	82
J	82
L	82
M	82
N	83
O	83
P	83
Q	83
R	83
S	83
T	84
U	84
V	84
W	84

Seagate ST300MM0026 Savvio 10K.1 SAS Product Manual - Page 20

Case B, Note., Caching write data

Page 20 highlights