Western Digital Purple PR1000M, Technical Reference Manual

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RODUCT
F
EATURES PR1000M
16 RELEASED 5/8/17 (WD CONFIDENTIAL) 2679-800020-A03
3.10 Native Command Queuing (NCQ )
These drives support Native Command Queuing. NCQ is a true Enterprise feature for
environments such as database, Web servers, and e-mail servers.
Performance of a random I/O workload can be improved through intelligent re-
ordering of the I/O requests so they read/write to and from the nearest available
sectors and minimize the need for additional disk revolutions or head actuator
movement. This improvement is achieved though Native Command Queuing (NCQ).
NCQ allows the drive to re-order read commands, thereby increasing random read
IOPs. Additional NCQ features that can prove beneficial include a Write Cache
disabled IOP increase and a queuing implementation built upon an existing, highly
automated cache architecture. Queued reads in NCQ leverage the same re-ordering
schemes used for write caching. The firmware design maintains the "order" of
overlapping/colliding queued commands. NCQ is designed to excel in multi-
threaded environments with high random I/O loads.
3.11 Pre-emptive Wear Leveling (PWL)
This WD feature provides a solution for protecting the recording media against
mechanical wear. In cases where the drive is so busy with incoming commands that
it is forced to stay in a same cylinder position for a long time, the PWL control engine
initiates forced seeks so that disk lubricant maintains an even distribution and does
not become depleted. This feature ensures reliability for applications that perform a
high incidence of read/write operations at the same physical location on the disk.
3.12 Femto Slider
These drives incorporate the femto slider form factor in which the read/write head is
mounted on the small, lightweight femto slider which allows the head to move more
quickly from track to track on the disk. WD’s femto heads enhance tracking and
increase shock tolerance, producing a highly stable high-density drive platform.
3.13 S.M.A.R.T. Command Transport (SCT)
The SCT Command Transport feature set provides a method for a host to send
commands and data to a device and for a device to send data and status to a host
using log pages. Standard ATA commands may be interspersed with SCT commands,
but SCT commands cannot be nested. SCT commands that do not require a
subsequent data transfer operation are not interspersed with any ATA commands or
each other.
The SCT Command Transport feature set provides a method for a host to send
commands and data to a device and for a device to send data and status to a host
using log pages. This capabilitility is used to pass commands through a driver
interface or a bridge where new or unknown commands may be filtered and not
passed to the drive. SCT is also used for issuing commands that require more than 8
parameter bytes. ATA8-ACS provides detailed information on the usage and
capabilities of SCT. The SCT feature set includes the following commands:

Write Same

Temperature Reporting
3.13.1 Write Same
The Write Same command allows the host to erase the media, or write a pattern
repeatedly across the media, with a minimum of data transfer from the host. The host
can clear the entire media to zeros or a specific pattern by sending this command