Seagate ST300MP0014 Savvio 15K.1 FC User Guide - Page 21

Savvio 15K.1 FC Product Manual, Rev. B

13

The START STOP UNIT command may be used to command the drive to stop the spindle. Stop time is 30 sec-

onds (maximum) from removal of DC power. There is no power control switch on the drive.

4.4

Prefetch/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 opera-

tion, the prefetch feature overlaps cache operation somewhat as described in sections 4.5.1 and 4.5.2.

4.5

Cache operation

Note.

Refer to the

Fibre Channel Interface Manual

for more detail concerning the cache bits.

Of the 16 Mbytes physical buffer space in the drive, approximately

13,000 Kbytes can be used as a cache. The

buffer can be 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


), data requested by the host with a read

command is retrieved from the buffer, if possible, before any disc access is initiated. If cache operation is not

enabled, the buffer (still segmented with the required number of segments) is still used, but only as circular

buffer segments during disc 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. On a

cache miss, all data transfers to the host are in accordance with buffer-full ratio rules. On a cache hit, the drive

ignores the buffer-full ratio rules. See the explanation provided with the information about Mode Page 02h (dis-

connect/reconnect control) in the


.

The following is a simplified description of the prefetch/cache operation:

Case A

—read command is received and the first logical block is already in the cache:

1.

Drive transfers the requested logical blocks to the initiator.

Case B

—A Read command requests data, and at least one requested 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.

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

blocks. The drive dynamically creates and removes segments based on the workload. The wrap-around capa-

bility of the individual segments greatly enhances the cache’s overall performance.

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.

Section	Page
1.0 Scope	9
2.0 Applicable standards and reference documentation	11
2.1 Standards	11
2.1.1 Electromagnetic compatibility	11
2.1.1.1 Electromagnetic susceptibility	11
2.1.2 Electromagnetic compliance	12
2.2 European Union Restriction of Hazardous Substances (RoHS)	12
2.3 Reference documents	13
3.0 General description	15
3.1 Standard features	16
3.2 Media description	17
3.3 Performance	17
3.4 Reliability	17
3.5 Formatted capacities	17
3.5.1 Programmable drive capacity	18
3.6 Factory-installed accessories	18
3.7 Options	18
4.0 Performance characteristics	19
4.1 Internal drive characteristics	19
4.2 Seek performance characteristics	19
4.2.1 Access time	19
4.2.2 Format command execution time	20
4.2.3 General performance characteristics	20
4.3 Start/stop time	20
4.4 Prefetch/multi-segmented cache control	21
4.5 Cache operation	21
4.5.1 Caching write data	21
4.5.2 Prefetch operation	22
5.0 Reliability specifications	23
5.1 Error rates	23
5.1.1 Recoverable Errors	23
5.1.2 Unrecoverable Errors	24
5.1.3 Seek errors	24
5.1.4 Interface errors	24
5.2 Reliability and service	24
5.2.1 Annualized Failure Rate (AFR) and Mean Time Between Failure (MTBF)	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	28
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	35
6.4 Environmental limits	38
6.4.1 Temperature	38
6.4.2 Relative humidity	39
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	42
6.4.5 Air cleanliness	42
6.4.6 Corrosive environment	42
6.4.7 Acoustics	43
6.4.8 Electromagnetic susceptibility	43
6.5 Mechanical specifications	44
7.0 Defect and error management	45
7.1 Drive internal defects/errors	45
7.2 Drive error recovery procedures	45
7.3 FC-AL system errors	46
7.4 Background Media Scan	47
7.5 Media Pre-Scan	47
7.6 Deferred Auto-Reallocation	47
7.7 Idle Read After Write	48
8.0 Installation	49
8.1 Drive orientation	49
8.2 Cooling	49
8.3 Drive mounting	50
8.4 Grounding	50
9.0 Interface requirements	51
9.1 FC-AL features	51
9.1.1 Fibre Channel link service frames	51
9.1.2 Fibre Channel task management functions	52
9.1.3 Fibre Channel task management responses	52
9.1.4 Fibre Channel port login	53
9.1.5 Fibre Channel port login accept	54
9.1.6 Fibre Channel Process Login	54
9.1.7 Fibre Channel Process Login Accept	55
9.1.8 Fibre Channel fabric login	55
9.1.9 Fibre Channel fabric accept login	56
9.1.10 Fibre Channel Arbitrated Loop options	57
9.2 Dual port support	57
9.3 SCSI commands supported	58
9.3.1 Inquiry data	63
9.4 Miscellaneous operating features and conditions	64
9.5 FC-AL physical interface	65
9.5.1 Physical characteristics	65
9.5.1.1 Physical description	65
9.5.2 Connector requirements	66
9.5.3 Electrical description	66
9.5.4 Pin descriptions	67
9.5.5 FC-AL transmitters and receivers	68
9.5.6 Power	68
9.5.7 Fault LED Out	68
9.5.8 Active LED Out	69
9.5.9 Enable port bypass signals	69
9.5.10 Motor start controls	69
9.5.11 SEL_6 through SEL_0 ID lines	70
9.5.11.1 Parallel Enclosure Services Interface (ESI)	70
9.5.12 Device control codes	72
9.6 Signal characteristics	72
9.6.1 TTL input characteristics	72
9.6.2 Differential PECL output	73
9.6.3 Differential PECL input	73

Seagate ST300MP0014 Savvio 15K.1 FC User Guide - Page 21

Prefetch/multi-segmented cache control, Cache operation

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