Publication number: 100865853, Rev. C January 2021
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When referring to drive capacity, one gigabyte, or GB, equals one billion bytes and one terabyte, or TB, equals one trillion bytes. Your computer’s operating system may use a different
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Actual quantities will vary based on various factors, including file size, file format, features and application software. Actual data rates may vary depending on operating environment
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Seagate Exos X18 SAS Product Manual, Rev. C 5
www.seagate.comScope
1.0Scope
This manual describes Seagate® Exos® X18 SAS (Serial Attached SCSI) disk drives.
Exos X18 drives support the SAS Protocol specifications to the extent described in this manual. The SAS Interface Manual (part number 100293071)
describes the general SAS characteristics of this and other Seagate SAS drives.
Product data communicated in this manual is specific only to the model numbers listed in this manual. The data listed in this manual may not be
predictive of future generation specifications or requirements. If designing a system which will use one of the models listed or future generation
products and need further assistance, please contact the Field Applications Engineer (FAE) or our global support services group as shown in
“Seagate® Technology Support Services” on page 5.
Unless otherwise stated, the information in this manual applies to standard and Self-Encrypting Drive models.
Model type5xxE
Standard
Self-Encrypting Drive (SED)
SED-FIPS 140-2
.
Note
The Self-Encrypting Drive models indicated on the cover of this product manual have provisions for “Security of Data
at Rest” based on the standards defined by the Trusted Computing Group (see www.trustedcomputinggroup.org).
www.seagate.comHDD and SSD Regulatory Compliance and Safety
2.0HDD and SSD Regulatory Compliance and Safety
For the latest regulatory and compliance information see:www.seagate.com/support
scroll down the page and click the Compliance, Safety and Disposal Guide link.
2.0.1Regulatory Models
The following regulatory model number represent all features and configurations within the series:
Regulatory Model Numbers: STL015
2.1Reference documents
SAS Interface Manual
SCSI Commands Reference Manual
Self-Encrypting Drives Reference Manual
ANSI SAS Documents
ANSI Small Computer System Interface (SCSI) Documents
Trusted Computing Group (TCG) Documents (apply to Self-Encrypting Drive models only)
Specification for Acoustic Test Requirement and Procedures
In case of conflict between this document and any referenced document, this document takes precedence.
Seagate Exos X18 SAS Product Manual, Rev. C7
www.seagate.comGeneral description
3.0General description
Exos X18 drives provide high performance, high capacity data storage for a variety of systems including engineering workstations, network
servers, mainframes, and supercomputers. The Serial Attached SCSI interface is designed to meet next-generation computing demands for
performance, scalability, flexibility and high-density storage requirements.
Exos X18 drives are random access storage devices designed to support the Serial Attached SCSI Protocol as described in the ANSI specifications,
this document, and the SAS Interface Manual (part number 100293071) which describes the general interface characteristics of this drive. Exos X18
drives are classified as intelligent peripherals and provide level 2 conformance (highest level) with the ANSI SCSI-1 standard. The SAS connectors,
cables and electrical interface are compatible with Serial ATA (SATA), giving future users the choice of populating their systems with either SAS or
SATA hard disk drives. This allows users to continue to leverage existing investment in SCSI while gaining a 12Gb/s serial data transfer rate.
The Self-Encrypting Drive models indicated on the cover of this product manual have provisions for “Security of Data at Rest” based on the
standards defined by the Trusted Computing Group
(see www.trustedcomputin
The head and disk assembly (HDA) is sealed at the factory. Helium recirculates within the HDA through a non-replaceable filter to maintain a
contamination-free HDA environment.
Note
An automatic shipping lock prevents potential damage to the heads and discs that results from movement during shipping and handling. The
shipping lock disengages and the head load process begins when power is applied to the drive.
Exos X18 drives decode track 0 location data from the servo data embedded on each surface to eliminate mechanical transducer adjustments and
related reliability concerns.
The drives also use a high-performance actuator assembly with a low-inertia, balanced, patented, straight arm design that provides excellent
performance with minimal power dissipation.
Note
Never disassemble the HDA and do not attempt to service items in the sealed enclosure
(heads, media, actuator, etc.) as this requires special facilities. The drive does not contain userreplaceable parts. Opening the HDA for any reason voids the product warranty.
Seagate recommends validating the configuration with the selected HBA/RAID controller
manufacturer to ensure use of full capacity is supported.
ggroup.org).
Seagate Exos X18 SAS Product Manual, Rev. C8
www.seagate.comGeneral description
3.1Standard features
Exos X18 drives have the following standard features:
• 128 - deep task set (queue)
• 256MB data buffer (See Section 4.4) .
• 3.0 / 6.0/12.0 Gb Serial Attached SCSI (SAS) interface
• Drive Self Test (DST)
• Embedded servo design
• Firmware downloadable using the SAS interface
• Flawed logical block reallocation at format time
• Idle Read After Write (IRAW)
• Industry standard SFF 3.5-in dimensions
• Integrated dual port SAS controller supporting the SCSI protocol
• Jumperless configuration.
• No preventive maintenance or adjustments required
• Perpendicular recording technology
• Power Balance supported (see Section 6.2 on page 23)
•Power Save
• Programmable auto write and read reallocation
• Programmable logical block reallocation scheme
• Reallocation of defects on command (Post Format)
•SAS Power Disable
• Self diagnostics performed when power is applied to the drive
• Support for SAS expanders and fanout adapters
• Supports up to 32 initiators
• T10 Fast Format supported (see Section 4.1.2)
• User-selectable logical block sizes for 4096 native models (4096, 4160 or 4224 bytes per logical block)
• User-selectable logical block sizes for 512E (512, 520 or 528 bytes per logical block).
• Vertical, horizontal, or top down mounting
Seagate Exos X18 SAS Self-Encrypting Drive models have the following additional features:
• 32 Independent data bands
• Authenticated firmware download
• Automatic data encryption/decryption
• Controlled access
• Cryptographic erase of user data for a drive that will be repurposed or scrapped
• Supports start and stop commands (spindle stops spinning)
.
Note
There is no significant performance difference between Self-Encrypting
Drive and standard (non-Self-Encrypting Drive) models.
3.3Reliability
• 5-year warranty
• Annualized Failure Rate (AFR) of 0.35%
• Balanced low mass rotary voice coil actuator
• Incorporates industry-standard Self-Monitoring Analysis and Reporting Technology (S.M.A.R.T.)
• Mean time between failures (MTBF) of 2,500,000 hours
Seagate Exos X18 SAS Product Manual, Rev. C9
www.seagate.comGeneral description
3.4Media description
The media used on the drive has a glass substrate coated with a thin film magnetic material, overcoated with a proprietary protective layer for
improved durability and environmental protection.
3.5Formatted capacities
Standard OEM models are formatted to 512 bytes per block for 512 emulation drives and 4096 bytes per block for 4096 native drives. The block
size is selectable at format time. Supported block sizes are 512, 520 and 528 for 512 emulation drives and 4096, 4160 and 4224 for 4096 native
drives. Users having the necessary equipment may modify the data block size before issuing a format command and obtain different formatted
capacities than those listed.
To provide a stable target capacity environment and at the same time provide users with flexibility if they choose, Seagate recommends product
planning in one of two modes:
Seagate designs specify capacity points at certain block sizes that Seagate guarantees current and future products will meet. We recommend
customers use this capacity in their project planning, as it ensures a stable operating point with backward and forward compatibility from
generation to generation. The current guaranteed operating points for this product are shown below.
LBA Counts for drive capacities greater than 8TB are calculated based upon
the SFF-8447 standard publication. ftp://ftp.seagate.com/sff/SFF-8447.PDF
www.seagate.comGeneral description
3.6Programmable drive capacity
Using the Mode Select command, the drive can change its capacity to something less than maximum. See the Mode Select (6) parameter list table
in the SAS Interface Manual, part number 100293071. A value of zero in the Number of Blocks field indicates that the drive will not change the
capacity it is currently formatted to have. A number other than zero and less than the maximum number of LBAs in the Number of Blocks field
changes the total drive capacity to the value in the Number of Blocks field. A value greater than the maximum number of LBAs is rounded down to
the maximum capacity.
3.7Factory-installed options
Users may order the following items which are incorporated at the manufacturing facility during production or packaged before shipping. Some
of the options available are (not an exhaustive list of possible options):
• Other capacities can be ordered depending on sparing scheme and sector size requested.
• Single-unit shipping pack. The drive is normally shipped in bulk packaging to provide maximum protection against transit damage. Units
shipped individually require additional protection as provided by the single unit shipping pack. Users planning single unit distribution should
specify this option.
•The Safety and Regulatory Agency Specifications, part number 75789512, is usually included with each standard OEM drive shipped, but extra
copies may be ordered.
Seagate Exos X18 SAS Product Manual, Rev. C11
www.seagate.comPerformance characteristics
4.0Performance characteristics
This section provides detailed information concerning performance-related characteristics and features of Exos X18 drives.
4.1Internal drive characteristics
Drive capacity18TB16TB14TB12TB(formatted, rounded off value)
Read/write data heads18171412
Bytes/track1,840,9431,785,9771,840,9431,704,382Bytes (average, rounded off values)
Bytes/surface1,000,000941,1761,000,000857,143MB (unformatted, rounded off values)
Tracks/surface (total)543,200526,981543,200502,905Tracks (user accessible)
Tracks/in482,000467,609482,000446,245TPI (average)
Peak bits/in2,470,0002,396,2512,470,0002,286,776BPI
Areal density1146112111461020Gb/in2
Internal data rate2899281228992684Mb/s (max)
Disk rotation speed7200720072007200RPM
Avg rotational latency4.164.164.164.16ms
Execution time measured from receipt of the last byte of the Command Descriptor Block (CDB) to the request for a Status Byte Transfer to the
Initiator (excluding connect/disconnect).
When changing sector sizes, the format times shown above may need to be increased by 30 minutes.
4.1.2Fast Format
Drive sector size transition
• Single code to support sector sizes from 512E
• T10 fast format conversion between 512E configurations in the field.
• Possible only if sector sizes are exact multiples of 8 & vice versa
• The selected sector size will take effect only after fast format or full format
• Drive default is 512E from the factory.
• 512E features set after Fast Format
T10 Fast Format
• Implements the fast format based on T10 Spec.
• To request Fast Format, the FFMT bits (Byte 4, Bits 1:0) should be set to 01b.
• A setting of 10b or 11b will return a check condition with 05/24 sense code (pointing to FFMT MSB in CDB).
Mode Select - Parameter list header
• Set Write buffer: // Set Block Descriptor Length = 0x08, Number of LBAs = 0xFFFFFFFF
• cdb: 04 14 00 00 01 00 // (FMTDAT = 1, DEFECT LIST FORMAT = 010b, FFMT = 01b)
Seagate Exos X18 SAS Product Manual, Rev. C12
www.seagate.comPerformance characteristics
4.1.3General performance characteristics
Minimum sector interleave1 to 1
Maximum Internal data rate*2.7 Gb/s
Sustained transfer rate103 to 258 MiB/s **
SAS Interface maximum instantaneous transfer rate1200MB/s* per port
Logical block sizes
512 (default), 520 or 528.
4096, 4160 or 4224.
Read/write consecutive sectors on a trackYes
Flaw reallocation performance impact (for flaws reallocated at format time using the spare
sectors per sparing zone reallocation scheme.)
Average rotational latency4.16ms
*Assumes no errors and no relocated logical blocks. Rate measured from the start of the first logical block transfer to or from the host.
** MiB/s x 1.048 = MB/s
(dual port = 2400MB/s*)
Negligible
4.2Start/stop time
Power-on to ready time is based on typical operating conditions, default full current spin-up profile, and clean shutdown prior to measurement.
To ensure a clean shutdown issue a START STOP UNIT command with the START bit set to zero and the IMMED bit set to zero, so that the device
will return status after the operation is completed.
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 23 seconds (maximum) from removal of DC
power. SCSI stop time is 23 seconds. There is no power control switch on the drive.
An unexpected power loss event, spin up at cold or hot temperature extremes may cause the drive to exceed the typical and max time to ready by
5 to 20 seconds. Extended time to ready is dependent on cache state and environmental conditions prior to the unexpected power loss and
during the subsequent power on.
Seagate Exos X18 SAS Product Manual, Rev. C13
www.seagate.comPerformance characteristics
4.3Prefetch/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 Table 4.4.1 and Table 4.4.2.
All default cache and prefetch mode parameter values (Mode Page 08h) for standard OEM versions of this drive family are given in Table 10.
4.4Cache operation
.
NoteRefer to the SAS Interface Manual for more detail concerning the cache bits.
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.
The following is a simplified description of the prefetch/cache operation:
Case A—read command is received and all of the requested logical blocks are 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 disk and transfers them into a segment, and then from there to the host in accor-
dance with the Mode Select Disconnect/Reconnect parameters, page 02h.
2.If the prefetch feature is enabled, refer to section Table 4.4.2 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 capability of the individual segments greatly enhances the cache’s overall
performance.
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.
Seagate Exos X18 SAS Product Manual, Rev. C14
www.seagate.comPerformance characteristics
4.4.1Caching 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 available 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 generated.
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 10 shows the mode default
settings for the drive.
4.4.2Prefetch operation
If the Prefetch feature is enabled, data in contiguous logical blocks on the disk 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 operation is disabled). Though the prefetch operation uses the buffer as a cache, finding the
requested data in the buffer is a prefetch hit, not a cache operation hit.
To enable Prefetch, use Mode Select page 08h, byte 12, bit 5 (Disable Read Ahead - DRA bit). DRA bit = 0 enables prefetch.
The drive does not use the Max Prefetch field (bytes 8 and 9) or the Prefetch Ceiling field (bytes 10 and 11).
When prefetch (read look-ahead) is enabled (enabled by DRA = 0), the drive enables prefetch of contiguous blocks from the disk when it senses
that a prefetch hit will likely occur. The drive disables prefetch when it decides that a prefetch hit is not likely to occur.
Seagate Exos X18 SAS Product Manual, Rev. C15
www.seagate.comReliability specifications
5.0Reliability specifications
The following reliability specifications assume correct host and drive operational interface, including all interface timings, power supply voltages,
environmental requirements and drive mounting constraints.
8
Seek error rate:Less than 10 errors in 10
Read Error Rates
1
Recovered DataLess than 10 errors in 1012 bits transferred (OEM default settings)
Unrecovered DataLess than 1 sector in 10
Miscorrected DataLess than 1 sector in 10
Interface error rate:Less than 1 error in 1012 bits transferred
Mean Time Between Failure (MTBF):2,500,000 hours
Annualized Failure Rate (AFR):
2
0.35%
Preventive maintenance:None required
1.Error rate specified with automatic retries and data correction with ECC enabled and all flaws reallocated.
2.See Section 5.2, "Reliability and service" for rated MTBF device operating condition requirements.
5.1Error rates
The error rates stated in this manual assume the following:
• The drive is operated in accordance with this manual using DC power as defined in Section 6.4, DC power requirements
• Errors caused by host system failures are excluded from error rate computations.
• Assume random data.
• Default OEM error recovery settings are applied. This includes AWRE, ARRE, full read retries, full write retries and full retry time.
seeks
15
bits transferred
21
bits transferred
5.1.1Recoverable Errors
Recoverable errors are those detected and corrected by the drive, and do not require user intervention.
Recoverable Data errors will use correction, although ECC on-the-fly is not considered for purposes of recovered error specifications.
Recovered Data error rate is determined using read bits transferred for recoverable errors occurring during a read, and using write bits transferred
for recoverable errors occurring during a write.
5.1.2Unrecoverable Errors
An unrecoverable data error is defined as a failure of the drive to recover data from the media. These errors occur due to head/media or write
problems. Unrecoverable data errors are only detected during read operations, but not caused by the read. If an unrecoverable data error is
detected, a MEDIUM ERROR (03h) in the Sense Key will be reported. Multiple unrecoverable data errors resulting from the same cause are treated
as 1 error.
5.1.3Seek errors
A seek error is defined as a failure of the drive to position the heads to the addressed track. After detecting an initial seek error, the drive
automatically performs an error recovery process. If the error recovery process fails, a seek positioning error (Error code = 15h or 02h) will be
reported with a Hardware error (04h) in the Sense Key. Recoverable seek errors are specified at Less than 10 errors in 10
8
seeks. Unrecoverable
seek errors (Sense Key = 04h) are classified as drive failures.
5.1.4Interface errors
An interface error is defined as a failure of the receiver on a port to recover the data as transmitted by the device port connected to the receiver.
The error may be detected as a running disparity error, illegal code, loss of word sync, or CRC error.
Seagate Exos X18 SAS Product Manual, Rev. C16
www.seagate.comReliability specifications
5.2Reliability and service
Users can enhance the reliability of Exos X18 disk drives by ensuring that the drive receives adequate cooling. Section 6.0 provides temperature
measurements and other information that may be used to enhance the service life of the drive. Section 9.2 provides recommended air-flow
information.
5.2.1Annualized Failure Rate (AFR) and Mean Time Between Failure (MTBF)
The production disk drive shall achieve an annualized failure-rate of 0.35% (MTBF of 2,500,000 hours) over a 5 year service life when used in
Enterprise Storage field conditions as limited by the following:
• 8760 power-on hours per year.
• HDA temperature as reported by the drive <= 30°C
• Ambient wet bulb temp <= 26°C
•Typical workload
• The AFR (MTBF) is a population statistic not relevant to individual units
• ANSI/ISA S71.04-2013 G2 classification levels and dust contamination to ISO 14644-1 Class 8 standards (as measured at the device)
The MTBF specification for the drive assumes the operating environment is designed to maintain nominal drive temperature and humidity.
Occasional excursions in operating conditions between the rated MTBF conditions and the maximum drive operating conditions may occur
without significant impact to the rated MTBF. However continual or sustained operation beyond the rated MTBF conditions will degrade the drive
MTBF and reduce product reliability.
15
Nonrecoverable read errors1 per 10
Load unload cycles600,000 cycles
bits read, max
Maximum Rated WorkloadMaximum rate of <550TB/year
Warranty
Preventive maintenanceNone required.
Workloads exceeding the annualized rate may degrade the drive MTBF and impact product
reliability. The Annualized Workload Rate is in units of TB per year, or TB per 8760 power on
hours. Workload Rate = TB transferred * (8760 / recorded power on hours).
To determine the warranty for a specific drive, use a web browser to access the following web
page: www.sea
From this page, click on the “Is my Drive under Warranty” link. The following are required to be
provided: the drive serial number, model number (or part number) and country of purchase.
The system will display the warranty information for the drive.
gate.com/support/warranty-and-replacements/.
5.2.2Hot plugging the drive
When a disk is powered on by switching the power or hot plugged, the drive runs a self test before attempting to communicate on its’ interfaces.
When the self test completes successfully, the drive initiates a Link Reset starting with OOB. An attached device should respond to the link reset. If
the link reset attempt fails, or any time the drive looses sync, the drive initiated link reset. The drive will initiate link reset once per second but
alternates between port A and B. Therefore each port will attempt a link reset once per 2 seconds assuming both ports are out of sync.
If the self-test fails, the drive does not respond to link reset on the failing port.
It is the responsibility of the systems integrator to assure that no temperature, energy, voltage hazard, or ESD potential hazard is presented during
the hot connect/disconnect operation. Discharge the static electricity from the drive carrier prior to inserting it into the system.
Caution
The drive motor must come to a complete stop prior to changing the
plane of operation. This time is required to insure data integrity.
Seagate Exos X18 SAS Product Manual, Rev. C17
www.seagate.comReliability specifications
5.2.3S.M.A.R.T.
S.M.A.R.T. is an acronym for Self-Monitoring Analysis and Reporting Technology. This technology is intended to recognize conditions that indicate
imminent drive failure and is designed to provide sufficient warning of a failure to allow users to back up the data before an actual failure occurs.
Note
Each monitored attribute has been selected to monitor a specific set of failure conditions in the operating performance of the drive and the
thresholds are optimized to minimize “false” and “failed” predictions.
The drive’s firmware monitors specific attributes for degradation
over time but can’t predict instantaneous drive failures.
Controlling S.M.A.R.T.
The operating mode of S.M.A.R.T. is controlled by the DEXCPT and PERF bits on the Informational Exceptions Control mode page (1Ch). Use the
DEXCPT bit to enable or disable the S.M.A.R.T. feature. Setting the DEXCPT bit disables all S.M.A.R.T. functions. When enabled, S.M.A.R.T. collects
on-line data as the drive performs normal read and write operations. When the PERF bit is set, the drive is considered to be in “On-line Mode Only”
and will not perform off-line functions.
Users can measure off-line attributes and force the drive to save the data by using the Rezero Unit command. Forcing S.M.A.R.T. resets the timer so
that the next scheduled interrupt is in one hour.
Users can interrogate the drive through the host to determine the time remaining before the next scheduled measurement and data logging
process occurs. To accomplish this, issue a Log Sense command to log page 0x3E. This allows the user to control when S.M.A.R.T. interruptions
occur. Forcing S.M.A.R.T. with the RTZ command resets the timer.
Performance impact
S.M.A.R.T. attribute data is saved to the disk so that the events that caused a predictive failure can be recreated. The drive measures and saves
parameters once every one hour subject to an idle period on the drive interfaces. The process of measuring off-line attribute data and saving data
to the disk is interruptible. The maximum on-line only processing delay is summarized below:
Maximum processing delay
Fully-enabled delay DEXCPT = 0
S.M.A.R.T. delay times75 ms
Reporting control
Reporting is controlled by the MRIE bits in the Informational Exceptions Control mode page (1Ch). An example, if the MRIE is set to one, the
firmware will issue to the host an 01-5D00 sense code. The FRU field contains the type of predictive failure that occurred. The error code is
preserved through bus resets and power cycles.
Determining rate
S.M.A.R.T. monitors the rate at which errors occur and signals a predictive failure if the rate of degraded errors increases to an unacceptable level.
To determine rate, error events are logged and compared to the number of total operations for a given attribute. The interval defines the number
of operations over which to measure the rate. The counter that keeps track of the current number of operations is referred to as the Interval
Counter.
S.M.A.R.T. measures error rates. All errors for each monitored attribute are recorded. A counter keeps track of the number of errors for the current
interval. This counter is referred to as the Failure Counter.
Error rate is the number of errors per operation. The algorithm that S.M.A.R.T. uses to record rates of error is to set thresholds for the number of
errors and their interval. If the number of errors exceeds the threshold before the interval expires, the error rate is considered to be unacceptable.
If the number of errors does not exceed the threshold before the interval expires, the error rate is considered to be acceptable. In either case, the
interval and failure counters are reset and the process starts over.
Seagate Exos X18 SAS Product Manual, Rev. C18
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