ISO/IEC 14776-326:2015

Information technology - Small computer system interface (SCSI) - Part 326: Reduced block commands (RBC)

ISO/IEC 14776-326:2015(E) defines a Reduced Block Command set for logical block devices. The Reduced Block Commands along with the required SPC-2 commands and their restrictions described in this standard, fully specify the complete command set for RBC logical block devices. It provides a command set of reduced requirements and options from SCSI Block Commands (SBC) (ISO/IEC 14776-321) for block devices. The reduced command set is intended to more closely match the functionality required for simple block logical units. The specified commands place no restrictions on device performance. The initial focus of this command set was to enable rigid disks and removable media devices attached to Serial Bus and utilizing SBP-2 (ISO/IEC 14776-232) for command and control. This second edition cancels and replaces the first edition published in 2002 and constitutes a minor revision. This second edition provides additional explanations and corrects mistakes with respect to the first edition.

General Information

• Status: Published
• Publication Date: 07-Sep-2015
• ICS: 35.200 - Interface and interconnection equipment
• Technical Committee: ISO/IEC JTC 1/SC 25 - Interconnection of information technology equipment
• Current Stage: PPUB - Publication issued
• Start Date: 08-Sep-2015
• Completion Date: 30-Nov-2015

Relations

• Revises: ISO/IEC 14776-326:2002/COR1:2009 - Corrigendum 1 - Information technology - Small computer system interface (SCSI) - Part 326: Reduced block commands (RBC)
• Effective Date: 05-Sep-2023
• Revises: ISO/IEC 14776-326:2002 - Information technology - Small computer system interface (SCSI) - Part 326: Reduced block commands (RBC)
• Effective Date: 05-Sep-2023

Overview

ISO/IEC 14776-326:2015 - Part 326 of the SCSI family - specifies the Reduced Block Commands (RBC) command set for logical block devices. This second edition (2015) is a minor revision of the 2002 edition that adds explanations and corrects errors. RBC defines a smaller, simpler SCSI block command subset together with required SPC‑2 commands and restrictions, to fully specify the command set for simple block logical units such as rigid disks and removable-media drives, particularly when attached via Serial Bus (SBP‑2). The standard does not place device performance constraints.

Key topics and technical requirements

• Reduced command set: A pared-down subset of SCSI Block Commands (SBC) tailored for simple block devices. Core commands defined include:
  • FORMAT UNIT, READ(10), WRITE(10), READ CAPACITY, START STOP UNIT
  • SYNCHRONIZE CACHE, VERIFY, and associated MODE parameter controls
• SPC‑2 implementation requirements: Specifies required SPC‑2 commands and how RBC devices must behave with standard SCSI protocol commands (e.g., INQUIRY, REQUEST SENSE, TEST UNIT READY).
• Device model and medium handling: Defines RBC device and removable-medium models, logical block semantics, medium removal prevention, and start/stop semantics.
• Error and event handling: Asynchronous event notification, unit attention, deferred errors, information exception conditions and event status reporting (including power and media class events).
• Reservations and concurrency: Rules for command permission in presence of reservations and how RBC commands interact with SCSI reservations.
• SBP‑2 normative annex: Annex A provides implementation requirements for devices using SBP‑2 (Serial Bus Protocol 2), covering configuration ROM, status blocks, unsolicited status, and reconnect/power reset support.

Applications and who uses this standard

• Storage device manufacturers designing firmware for simple block devices (rigid disks, removable drives) that target Serial Bus/FireWire or similar transport using SBP‑2.
• Firmware and driver developers implementing RBC and SPC‑2 behaviors for device controllers and operating system drivers.
• System integrators and OEMs needing a compact SCSI command set for low-complexity storage targets.
• Compliance test labs and QA engineers validating SCSI/SBP‑2 interoperability, event reporting, and reservation behavior.
• Technical writers and standards engineers documenting device capabilities and conformance to SCSI block command profiles.

Related standards

• ISO/IEC 14776-321 - SCSI Block Commands (SBC) - full block command set (reference for differences)
• ISO/IEC 14776-232 - SBP‑2 (Serial Bus Protocol 2) - transport-specific requirements for RBC over Serial Bus
• SPC‑2 (SCSI Primary Commands - set of common command requirements referenced by RBC)

Keywords: ISO/IEC 14776-326:2015, Reduced Block Commands, RBC, SCSI, SBP-2, SPC-2, block devices, removable media, SCSI command set.

Standards Content (Sample)

ISO/IEC 14776-326
Edition 2.0 2015-09
INTERNATIONAL
STANDARD
Information technology – Small computer system interface (SCSI) –
Part 326: Reduced block commands (RBC)

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ISO/IEC 14776-326
Edition 2.0 2015-09
INTERNATIONAL
STANDARD
Information technology – Small computer system interface (SCSI) –

Part 326: Reduced block commands (RBC)

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 35.200 ISBN 978-2-8322-2861-6

– 2 – ISO/IEC 14776-326:2015 © ISO/IEC 2015
CONTENTS
FOREWORD . 5
1 Scope . 6
2 Normative references . 6
3 Terms, definitions, abbreviations, keywords, and conventions . 7
3.1 Terms and definitions . 7
3.2 Abbreviations . 8
3.3 Keywords . 8
3.4 Conventions . 9
3.4.1 Non-numeric values . 9
3.4.2 Numeric values . 10
4 RBC device model . 10
4.1 General . 10
4.2 Removable medium device . 10
4.3 Command usage . 11
4.3.1 General . 11
4.3.2 Using the INQUIRY command . 11
4.3.3 Using the REQUEST SENSE command . 11
4.3.4 FORMAT UNIT command progress determination . 11
4.4 Using the PREVENT ALLOW MEDIUM REMOVAL command . 12
4.4.1 General . 12
4.4.2 START STOP UNIT command state restrictions . 12
4.5 Logical Blocks . 12
4.6 Reservations . 13
5 Reduced Block Commands . 14
5.1 General . 14
5.2 FORMAT UNIT command . 16
5.3 READ(10) Command . 17
5.4 READ CAPACITY command . 17
5.5 START STOP UNIT command . 18
5.5.1 General . 18
5.5.2 Power conditions . 19
5.5.3 Enable/Disable bits . 20
5.6 SYNCHRONIZE CACHE command . 21
5.7 VERIFY command . 21
5.8 WRITE(10) command . 22
5.9 Mode parameters . 23
5.9.1 General . 23
5.9.2 Mode parameter list . 23
5.9.3 Mode Parameter header . 23
5.9.4 RBC Device Parameter's page . 23
6 SPC-2 implementation requirements for RBC devices . 25
6.1 General . 25
6.2 INQUIRY command . 25
6.2.1 Standard INQUIRY data . 25
6.2.2 INQUIRY vital product data pages . 26
6.3 MODE SELECT(6) command . 27

6.4 MODE SENSE(6) command . 27
6.5 PREVENT ALLOW MEDIUM REMOVAL . 28
6.6 REQUEST SENSE command . 28
6.7 TEST UNIT READY command . 28
6.8 WRITE BUFFER Command . 29
6.8.1 General . 29
6.8.2 Download microcode and save mode (101b) . 30
6.8.3 Download microcode with offsets and save mode (111b) . 30
7 Asynchronous event notification for RBC devices . 30
7.1 General . 30
7.2 Unit attention . 31
7.2.1 General . 31
7.2.2 Power condition change notification . 31
7.3 Deferred errors . 31
7.4 Information exception condition notification . 31
7.5 Event status notification . 31
7.5.1 General . 31
7.5.2 Event Status sense information . 32
7.5.3 Power Management CLASS event INFORMATION field . 32
7.5.4 MEDIA CLASS EVENT INFORMATION field . 33
7.5.5 DEVICE BUSY CLASS EVENT INFORMATION field . 34
7.5.6 Event status retention . 35
7.5.7 Removable medium device initial response . 35
Annex A (normative) RBC device implementation requirements for SBP-2 . 36
A.1 SBP-2 terms and definitions . 36
A.1.1 Terms and definitions . 36
A.1.2 Abbreviations . 38
A.2 SBP-2 storage model . 38
A.2.1 General . 38
A.2.2 Model configuration . 38
A.2.3 Reconnect/Power reset support . 40
A.3 Configuration ROM support . 40
A.3.1 General . 40
A.3.2 Unit Directory – Command_Set_Spec_ID . 40
A.3.3 Unit Directory – Command_Set . 41
A.3.4 Unit Directory – Logical_Unit_Number . 41
A.4 Security support . 41
A.5 Status block support . 41
A.6 Unsolicited Status support . 42
A.6.1 General . 42
A.6.2 Unit attention condition . 42
A.6.3 Event Status retention . 42

Figure A.1 – Mass storage interface block diagram . 39
Figure A.2 – Status block for RBC. 42

Table 1 – RBC direct access commands that are allowed in the presence of various
reservations . 14

– 4 – ISO/IEC 14776-326:2015 © ISO/IEC 2015
Table 2 – Reduced Block Command set . 15
Table 3 – FORMAT UNIT command . 16
Table 4 – READ (10) Command Descriptor Block. 17
Table 5 – READ CAPACITY Command Descriptor Block . 18
Table 6 – READ CAPACITY data . 18
Table 7 – START STOP UNIT Command Descriptor Block . 19
Table 8 – POWER CONDITIONS . 19
Table 9 – START STOP control bit definitions . 21
Table 10 – SYNCHRONIZE CACHE Command Descriptor Block . 21
Table 11 – VERIFY Command Descriptor Block . 22
Table 12 – WRITE(10) Command Descriptor Block . 22
Table 13 – Mode parameter list . 23
Table 14 – RBC Device Parameters page format . 24
Table 15 – Required SPC-2 commands. 25
Table 16 – Standard Inquiry data format . 26
Table 17 – MODE SELECT(6) Command Descriptor Block . 27
Table 18 – MODE SENSE(6) Command Descriptor Block . 28
Table 19 – FAILURE PREDICTION ASCQ XY definitions . 29
Table 20 – WRITE BUFFER Command Descriptor Block . 29
Table 21 – Asynchronous Event conditions . 30
Table 22 – Power condition sense code and qualifier values . 31
Table 23 – Event status ASCQ values. 32
Table 24 – Event Status INFORMATION field format . 32
Table 25 – POWER MANAGEMENT CLASS EVENT INFORMATION field format . 32
Table 26 – POWER MANAGEMENT CLASS EVENT EVENT field . 33
Table 27 – POWER MANAGEMENT CLASS EVENT STATUS field . 33
Table 28 – MEDIA CLASS EVENT INFORMATION field format . 33
Table 29 – MEDIA CLASS EVENT EVENT field . 34
Table 30 – DEVICE BUSY CLASS EVENT information field format . 34
Table 31 – DEVICE BUSY CLASS EVENT EVENT field . 34
Table 32 – DEVICE BUSY CLASS STATUS field . 35

INFORMATION TECHNOLOGY –
SMALL COMPUTER SYSTEM INTERFACE (SCSI) –

Part 326: Reduced block commands (RBC)

FOREWORD
1) ISO (the International Organization for Standardization) and IEC (the International Electrotechnical Commission)
form the specialized system for worldwide standardization. National bodies that are members of ISO or IEC
participate in the development of International Standards through technical committees established by the
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2) The formal decisions or agreements of IEC and ISO on technical matters express, as nearly as possible, an
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9) Attention is drawn to the possibility that some of the elements of this ISO/IEC publication may be the subject of
patent rights. ISO and IEC shall not be held responsible for identifying any or all such patent rights.
International Standard ISO/IEC 14776-326 was prepared by subcommittee 25: Interconnection
of information technology equipment, of ISO/IEC joint technical committee 1: Information
technology.
This second edition cancels and replaces the first edition published in 2002 and constitutes a
minor revision.
This second edition provides additional explanations and corrects mistakes with respect to the
first edition.
A list of all parts in the ISO/IEC 14776 series, published under the general title Information
technology – Small computer system interface (SCSI), can be found on the IEC website.
This International Standard has been approved by vote of the member bodies, and the voting
results may be obtained from the address given on the second title page.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.

– 6 – ISO/IEC 14776-326:2015 © ISO/IEC 2015
INFORMATION TECHNOLOGY –
SMALL COMPUTER SYSTEM INTERFACE –

Part 326: Reduced block commands (RBC)

1 Scope
This part of ISO/IEC 14776 defines a Reduced Block Command set for logical block devices.
The Reduced Block Commands along with the required SPC-2 commands and their
restrictions described in this standard, fully specify the complete command set for RBC logical
block devices.
The purpose of this part of ISO/IEC 14776 is to provide a command set of reduced
requirements and options from SCSI Block Commands (SBC) (ISO/IEC 14776-321) for block
devices. The reduced command set is intended to more closely match the functionality
required for simple block logical units. The specified commands place no restrictions on
device performance. The initial focus of this command set was to enable rigid disks and
removable media devices attached to Serial Bus and utilizing SBP-2 (ISO/IEC 14776-232) for
command and control.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any
amendments) applies.
ISO/IEC 13213:1994, Information technology – Micoprocessor systems – Control and Status
Registers (CSR) Architecture for microcomputer buses
ISO/IEC 14776-232:2001, Information technology – Small computer system interface (SCSI)
– Part 232: Serial Bus Protocol 2 (SBP-2)
ISO/IEC 14776-321:2001, Information technology – Small Computer System Interface
(SCSI-3) – Part 321: Block commands (SBC)
ISO/IEC 14776-362:2006, Information technology – Small computer system interface (SCSI)
– Part 362: Multimedia commands-2 (MMC-2)
ISO/IEC14776-412, Information technology – Small computer system interface (SCSI) – Part
412: SCSI, Architecture model-2 (SAM-2)
ISO/IEC 14776-452:2005, Information technology – Small computer system interface (SCSI)
– Part 452: Primary commands-2 (SPC-2)
IEEE Standard 1394-1995, High Performance Serial Bus
IEEE Standard 1394A-2000, High Performance Serial Bus Amendment 1

3 Terms, definitions, abbreviations, keywords, and conventions
3.1 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1.1
additional sense code
ASC
field in the sense data
Note 1 to entry: See 7.20.2 in ISO/IEC 14776-452:2005.
[SOURCE: ISO/IEC 14776-452:2005, 3.1.2, modified – Reference to SPC-2 added.]
3.1.2
additional sense code qualifier
ASCQ
field in the sense data
Note 1 to entry: See 7.20.2 in ISO/IEC 14776-452:2005.
3.1.3
byte
B
eight bit of data
[SOURCE: ISO/IEC 14776-452:2005, 3.1.9, modified – Definition simplified.]
3.1.4
command descriptor block
CDB
structure of up to 16 B in length used to communicate a command from an initiator to a device
[SOURCE: ISO/IEC 14776-452:2005, 3.1.11, modified – Definition changed.]
3.1.5
EVENT field
byte 0 of the sense data INFORMATION field
Note 1 to entry: See Table 24 for the Event Status INFORMATION field format when the sense code indicates
EVENT STATUS NOTIFICATION (38h).
3.1.6
logical unit
part of the device that is an instance of a device model
Note 1 to entry: For example mass storage, CD-ROM or a printer are device models.
Note 2 to entry: In devices that implement one or more logical units, the device type of the logical units may
differ.
[SOURCE: ISO/IEC 14776-452:2005, 3.1.30, modified – Definition and explanatory
information changed.]
3.1.7
sense data
data describing an error or exceptional device condition that a device delivers to an initiator

– 8 – ISO/IEC 14776-326:2015 © ISO/IEC 2015
[SOURCE: ISO/IEC 14776-452:2005, 3.1.47, modified – Definition simplified and explanatory
information deleted.]
3.1.8
sense key
field in the sense data
Note 1 to entry: See 7.20.3 in ISO/IEC 14776-452.
[SOURCE: ISO/IEC 14776-452:2005, 3.1.48, modified – Definition changed.]
3.1.9
status
response information sent from a device to an initiator upon completion of each command
[SOURCE: ISO/IEC 14776-452:2005, 3.1.52, modified – Definition simplified and explanatory
information deleted.]
3.1.10
unit attention condition
condition that a logical unit maintains while it has asynchronous status information to report to
one or more initiators
[SOURCE: ISO/IEC 14776-452:2005, 3.1.58, modified – "State" has been replaced by
"condition" and refence information has been deleted.]
3.1.11
vendor specific
bit, field, code value, etc., not defined in this standard, that may be vendor defined
[SOURCE: ISO/IEC 14776-452:2005, 3.1.59, modified – Minor editorial change of the
definition.]
3.2 Abbreviations
The following abbreviations are used in this standard:
ASC Additional Sense Code
ASCQ Additional Sense Code Qualifier
CDB Command Descriptor Block
MMC-2 Multi-Medial Commands 2
RBC Reduced Block Commands (this standard)
SAM-2 SCSI Architecture Model 2
SBC SCSI Block Commands
SBP-2 Serial Bus Protocol 2
SPC-2 SCSI Primary Commands 2
3.3 Keywords
Several keywords are used to differentiate levels of requirements and options, as follows.
3.3.1
expected
keyword used to describe the behavior of the hardware or software in the design models
assumed by this standard. Other hardware and software design models may also be
implemented.
3.3.2
ignored
keyword that describes bits, bytes, quadlets, or fields whose values are not checked by the
recipient
3.3.3
mandatory
keyword that indicates items required to be implemented as defined by this standard
3.3.4
may
keyword that indicates flexibility of choice with no implied preference
3.3.5
optional
keyword that describes features which are not required to be implemented by this standard.
However, if any optional feature defined by the standard is implemented, it shall be
implemented as defined by the standard.
3.3.6
reserved
keyword used to describe objects (eg., bits, bytes, and field) or the code values assigned to
these objects in cases where either the object or the code value is set aside for future
standardization. Usage and interpretation may be specified by future extensions to this or
other standards. A reserved object shall be zeroed or, upon development of a future standard,
set to a value specified by such a standard. The recipient of a reserved object shall not check
its value. The recipient of a defined object shall check its value and reject reserved code
values.
3.3.7
shall
keyword that indicates a mandatory requirement. Designers are required to implement all
such mandatory requirements to assure interoperability with other products conforming to this
standard.
3.4 Conventions
The following conventions shall be understood by the reader in order to comprehend this
standard.
3.4.1 Non-numeric values
Lowercase is used for words having the normal English meaning. Certain words and terms
used in this standard have a specific meaning beyond the normal English meaning. These
words and terms are defined either in Clause 3 or in the text where they first appear.
The names of abbreviations, commands, and acronyms are in all uppercase (e.g., TEST UNIT
READY command).
Fields are shown in small caps (e.g., LOGICAL BLOCK ADDRESS).
Fields containing only one bit are usually referred to as the NAME bit instead of the NAME field.
Formal lists connoted by letters (e.g., a) red; b) blue; c) green) are in an arbitrary order.
Formal lists connoted by numbers (e.g., 1) red; 2) blue; 3) green) are in a required sequential
order.
– 10 – ISO/IEC 14776-326:2015 © ISO/IEC 2015
If a conflict arises between text, tables, or figures, the order of precedence to resolve conflicts
is text; then tables; and finally figures. Not all tables or figures are fully described in text.
Tables show data format and values. Notes do not constitute any requirements for
implementations.
3.4.2 Numeric values
The ISO convention of numbering is used (i.e., the thousands and higher multiples are
separated by a space and a comma is used as the decimal point as in 65 536 or 0,5).
Decimal numbers are represented by Arabic numerals without subscripts or by their English
names (e.g., 42, or twelve).
Hexadecimal numbers are represented by digits from the character set 0 to 9 and A to F
followed by the lower-case h (e.g., 2Ah).
Binary numbers are represented by digits from the character set 0 and 1 followed by the
lower-case b (e.g., 0010 1010b).
The most significant bit of a binary quantity is shown on the left side and represents the
highest algebraic value position in the quantity.
For the sake of legibility, binary and hexadecimal numbers are separated into groups of four
digits separated by spaces.
4 RBC device model
4.1 General
RBC logical units store blocks of data for later retrieval. Each block of data is stored at a
unique location. Initiators send WRITE commands to store the blocks of data (i.e., write
operations) and READ commands to retrieve the blocks of data (i.e., read operations). Other
commands sent by the initiator may cause write and read operations to occur.
A write operation causes one or more blocks of data to be written on the medium. A read
operation causes one or more blocks of data to be read from the medium. A verify operation
confirms that one or more blocks of data were correctly written and may be read without error
from the medium.
Blocks of data are stored by a process that causes localized changes or transitions within the
medium. The changes made to the medium to store the blocks of data may be volatile (i.e.,
not retained through off/on power cycles) or non-volatile (retained through off/on power
cycles). The medium may be divided in parts that are used for data blocks, parts that are
reserved for defect management, and parts that are reserved for use by the target for the
management of the logical unit.
4.2 Removable medium device
The medium in a RBC device may be removable (e.g., used in a floppy disk drive) or non-
removable (e.g. used in a fixed disk drive). Typically, removable medium is contained within a
cartridge (or jacket) to prevent damage to the recording surfaces.
A removable medium has an attribute of being mounted or de-mounted on a suitable transport
mechanism. A removable medium is mounted when the device/media combination is capable
of performing write or read operations and the initiator is informed of this status. A removable
medium is de-mounted at any other time (e.g., during loading, unloading, or storage).

Initiators may determine whether a RBC removable medium device is capable of performing
read or write operations by one of three methods:
a) enabling Asynchronous Event Reporting (see SPC-2) in the device and examining the
event information transmitted from the device;
b) issuing a TEST UNIT READY command and examining the returned status information; or
c) issuing a MODE SENSE command for Mode Page 06h (see 5.9.4) and examining the
state of the READD bit or WRITED bit. If the READD bit is set to one, then the media is not
readable. If the WRITED bit is set to one, then the media is not writable.
Until the RBC removable medium device and media are ready to be accessed, a READ(10)
command shall cause the device to return status of CHECK CONDITION (02h), sense key of
NOT READY (02h), and an ASC of LOGICAL UNIT NOT READY (04h). The ASCQ shall
reflect the current state of the device/media.
When the device becomes ready, a unit attention condition shall be established. The sense
key value shall be set to UNIT ATTENTION (06h), and the ASC/ASCQ to event STATUS
NOTIFICATION/MEDIA CLASS EVENT (38h/04h). The EVENT field contained within the sense
data INFORMATION field shall be set to NEW MEDIA READY FOR ACCESS (02h). When the
unit attention condition is delivered to the initiator, the status shall be set to CHECK
CONDITION (02h).
4.3 Command usage
4.3.1 General
RBC devices are not required to support the REQUEST SENSE command or the SEND
DIAGNOSTIC command. Devices that do not provide the Auto Sense function, Asynchronous
Event Reporting, or the GET EVENT/STATUS NOTIFICATION command (see MMC-2) shall
implement the REQUEST SENSE command.
All sense key, ASC, and ASCQ names and values contained in this standard are defined in
SPC-2. No additional or alternative meaning is intended by the use of such names and values
in this standard.
4.3.2 Using the INQUIRY command
The INQUIRY command (see SPC-2 and 6.2) may be used by an initiator to determine the
configuration of a logical unit. RBC devices return information that includes type and standard
version. The device may also return the vendor identification number, model number, and
other vendor specific information. It is recommended that devices provide the capability to
return this information upon completing power-on initialization. A device may take more time
to return certain portions of this information, especially if the information shall be retrieved
from the medium.
4.3.3 Using the REQUEST SENSE command
Whenever a command completes with CHECK CONDITION status and Auto Sense data is not
provided, the initiator that received the error status should send a REQUEST SENSE
command to acquire the sense data describing the cause of the condition. If the initiator
sends a command other than REQUEST SENSE, the sense data is lost.
Devices may be required to support the REQUEST SENSE command if they are unable to
provide command progress information by any other method.
4.3.4 FORMAT UNIT command progress determination
The FORMAT UNIT command (see 5.2) requires IMMED bit support because it may consume
significantly more time to complete than normal read or write commands. If the IMMED bit is set
to one, the device is required to return status as soon as the command descriptor block is

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validated. The device then completes the format operation. Initiators may determine the
progress of the format operation in several ways.
RBC devices may provide format progress information using one of the following methods:
a) progress is reported via Asynchronous Event Reporting. If the initiator and device support
this feature, the RBC device initiates progress reporting;
b) progress is reported via the GET EVENT/STATUS NOTIFICATION (see MMC-2)
command. Following the return of GOOD status, the initiator may poll the device for
command progress by issuing a GET EVENT/STATUS NOTIFICATION command. The
returned data contains progress information as defined in 7.5.6; or
c) progress is reported via the PROGRESS INDICATION field in the sense-key specific bytes of
REQUEST SENSE command sense data. See the SPC-2 standard for a description of this
method.
The first two methods return data in the Event Status Notification format described in 7.5.6.
4.4 Using the PREVENT ALLOW MEDIUM REMOVAL command
4.4.1 General
The PREVENT ALLOW MEDIUM REMOVAL command (see SPC-2) allows an initiator to
restrict the de-mounting of the medium. This is useful in maintaining system integrity. If the
removable medium device implements a cache, the command allows the initiator to ensure
that all logical blocks of the medium contain the most recent data prior to permitting de-
mounting of the removable medium.
If the initiator issues a START STOP UNIT command (see 5.5) to eject the cartridge, and the
removable medium device is prevented from de-mounting by the PREVENT ALLOW MEDIUM
REMOVAL command, the START STOP unit command is rejected by the device.
If the RMB bit is set to zero in the standard INQUIRY command data (see 6.2.1), the
PREVENT ALLOW MEDIUM REMOVAL command may not be supported. If the RMB bit is set
to one in the standard INQUIRY command data (see 6.2.1), the PREVENT ALLOW MEDIUM
REMOVAL command is supported (see 6.5).
4.4.2 START STOP UNIT command state restrictions
A removable medium device shall be in Prevent state 00b or 10b (see SPC-2) in order to
successfully process a START STOP UNIT command (see 5.5) with the POWER CONDITIONS
field (see Table 8) set to the Sleep power condition (i.e., 5h).
If a removable medium device in Prevent state 01b or 11b receives a START STOP UNIT
command with the POWER CONDITIONS field set to the Sleep power condition, the device shall
respond with status set to CHECK CONDITION (02h), the sense key to ILLEGAL REQUEST
(05h), and the ASC/ASCQ to ILLEGAL POWER CONDITION REQUEST (2Ch/05h).
A removable medium device in the Sleep power condition shall eject the media without
causing the media to spin up in accordance with the PREVENT/ALLOW MEDIUM REMOVAL
command requirements (see SPC-2).
See Table 8 for a description of the POWER CONDITIONS field values.
4.5 Logical Blocks
Data are addressed on the RBC device in a group referred to as a logical block. This is a
common attribute of RBC devices in that they are block addressable only.

Blocks of data are stored on the medium along with additional information that the medium
controller uses to manage the storage and retrieval of the blocks. The format of the additional
information is defined by other standards or is vendor specific and is hidden from the
application client during normal read or write operations.
The address of the first logical block is zero. The address of the last logical block is [n-1],
where [n] is the number of logical blocks available on the medium. A READ CAPACITY
command (see 5.4) may be used to determine the value of [n-1].
If a command is issued that requests access to a logical block not within the capacity of the
medium, the command is terminated with a status of CHECK CONDITION (02h), a sense key
of ILLEGAL REQUEST (05h), and an ASC/ASCQ of LOGICAL BLOCK ADDRESS OUT OF
RANGE (21h/00h).
The number of bytes of data contained in a logical block is known as the block length. Each
logical block has a block length associated with it. The block length is almost always greater
than one byte and is typically (but by no means always) a multiple of 512 B. In addition, a
logical block does not necessarily bear any relation to the physical block size of the storage
medium.
The LOGICAL BLOCK SIZE field in the RBC Device Parameters MODE SENSE page (see 5.9.4)
describes the block length that is used on the medium. A MODE SELECT command may be
used to set the logical block size, if the field is changeable.
The default NUMBER OF LOGICAL BLOCKS value may be obtained by requesting the default
MODE SENSE data (see SPC-2) for the RBC Device Parameters MODE SENSE page. The
current NUMBER OF LOGICAL BLOCKS value may be obtained by requesting the saved MODE
SENSE data for this page.
The location of a logical block on the medium does not necessarily have a relationship to the
location of any other logical block. However, in a typical logical unit the logical blocks are
located in an ascending order. The time to access the logical block at address [x] and then
the logical block at address [x+1] need not be less than time to access [x] and then [x+100].
4.6 Reservations
If the bus protocol does not inherently provide the ability to reserve and release access to a
device, then this function may be supported by the RESERVE command and the RELEASE
command (see SPC-2).
Reservation restrictions are placed on commands as a result of access qualifiers associated
with the type of reservation.
The details of what commands are allowed under what types of reservations are described in
Table 1. For the reservation restrictions placed on commands for the Reserve/Release
management method, see Table 1 column [A]. For the reservation restrictions placed on
commands for the Persistent Reservations management method, see Table 1 column [B].
In Table 1, the following key words are used:
allowed: Commands issued by initiators not holding the reservation or by initiators not
registered when a registrants only persistent reservation is present should complete normally.
conflict: Commands issued by initiators not holding the reservation or by initiators not
registered when a registrants only persistent reservation is present shall not be performed
and the device server shall terminate the command with a RESERVATION CONFLICT status.

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Commands from initiators holding a reservation should complete normally. The behavior of
commands from registered initiators when a registrants only persistent reservation is present
is specified in Table 1.
A command that does not explicitly write the medium shall be checked for reservation
conflicts before the command enters the current task state for the first time. Once the
command has entered the current task state (see SAM-2), it shall not be terminated with a
RESERVATION CONFLICT due to a subsequent reservation.
A command that explicitly writes the medium shall be checked for reservation conflicts, before
the device server modifies the medium or cache as a result of the command. Once the
command has modified the medium, it shall not be terminated with a RESERVATION
CONFLICT due to a subsequent reservation.
For each command, this standard, SPC-2, or a related command standard defines the
conditions that result in RESERVATION CONFLICT. Depending on the particular command
standard the conditions are defined in that standard’s device model clause or in the clauses
that define the specific commands.
Table 1 – RBC direct access commands that are
allowed in the presence of various reservations
Command Addressed Addressed LU has this type of persistent reservation
LU is held by another Initiator
reserved (B)
by another
From any Initiator From From Initiator not
Initiator
registered registered
(A)
Initiator
Write Excl Write Excl
...