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The SATA host adapter contains a set of registers that shadow the contents of the traditional device registers, referred to as
the Shadow Register Block. All SATA devices behave like Device 0 devices. For additional information about how SATA
emulates parallel ATA, refer to the "Serial ATA International Organization: Serial ATA Revision 3.2". The specification can be
downloaded from www.sata-io.org.
The host adapter may, optionally, emulate a master/slave environment to host software where two devices
on separate SATA ports are represented to host software as a Device 0 (master) and Device 1 (slave)
Note
accessed at the same set of host bus addresses. A host adapter that emulates a master/slave environment
manages two sets of shadow registers. This is not a typical SATA environment.
1.2 Zone Structure
NAS HDD models use SMR (Singled Magnetic Recording Technology), physically formatted containing two types of zones.
64 "Conventional Zones" which are not associated with write pointer, and the media is non-SMR and 29808 Sequential
Write preferred Zones which are SMR media. For the sequential write referred zones there is write pointer to indicated
preferred write location. For the conventional zone writes can occur randomly for any block size. New commands which
report zonal structure, resetting zonal write pointers, as well as managing zonal properties are available for sequential
write preferred zones through ZAC commands.
NAS HDD Conventional Zone Structure
•
There are 64 256Bi Conventional Zones. (ie. Not Singled)
•
The conventional zone is located at the outer diameter and is 16GBi
•
Sequential Read and Writes to this zones will perform at similar data rates.
•
Random Write commands can be issued in any order without any performance delay.
•
Zone designed specifically for random writes data. For example: logs and meta data.
There are 29808 Sequential Write Zones
•
Each zone is 2e19 logical blocks in size or 256 MiB each.
•
Each zone is a shingled zone.
•
To achieve best performance use of ZAC commands is required.
•
Re-setting write pointers for each zone is required before reuse.
Optimal number of open sequential write preferred zones
•
Advised the largest number of zones that should be open for best performance
•
It is reported in Identify Device Data log 0x30 page 0x09
Optimal number of non-sequentially written sequential write preferred zones
•
Advised the largest number of write preferred zones that should be randomly written for best performance
It is reported in identify device data log 0x30 page 0x0
T-13 standards define the new ZAC commands; REPORT ZONES EXT to query the drive on what zones exist and their
current condition, RESET WRITE POINTER EXT to reset the write pointers, OPEN ZONE EXT, CLOSE ZONE EXT, and FINISH
ZONE EXT to Open, Close, and Finish zones. To achieve optimal performance, an SMR-aware Host driver will need to write
sequentially to all sequential write referred zones.
See the T13 Web Site at http://www.t13.org for ACS-4, T13/BSR INCIT 529 for command details.
Seagate NAS HDD Product Manual, Rev. C
Introduction
6
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