Fea tu re D es cri pt io ns
Maxtor Atlas 10K III 6-3
The drive supports write-back caching. In this case, writes are considered complete
when the data is loaded into the cache, before it is written to the media. This allows
the host to go on to other tasks, while the drive assumes responsibility for the data and
ensuring that it is written to m edia as soon as possible. If write-back caching is
employed, it is recommended that an unint errupt ible power source (UPS) be
pro v i ded fo r opti m a l data s e cur i ty.
An aver age of half a r evol ut ion of latency i s saved by star t i ng to re ad or writ e as soon
as a seek settles on the designate d track. If reading, the initial data read is stored in a
buffer (cache) until the actual starting address data block is reached and read. The
starting address data is then transferred to the bus as the rest of the data is transferring
from media t o the buffer. When the initial data address read is reached again, that dat a
in the buffer is transferred to the bus. This ensures that the track data goes out in media
order and eliminates the rotationa l latency associated with waiting for the starting
add r es s to rotate to th e head.
Writing works essent iall y the same way only in reverse. The data is first transferred to
the drive's buffer. After seeking to the desired track, a write pointer is set to the current
locati on of the head on the track and wr iting is c ommenced from the buf fer, sta r ting
at the corresponding place in the data.
System throughput can be improved by disconnecting the drive from the initiator
during physical positioning operations, thereby freeing up the SCSI bus for other I/
O processes. After the drive has determined that there will be a delay, it disconnects
itself from the SC SI bus by sending a DISCONNEC T message and enters the BUS
FR E E p h as e.
When the drive is ready to resume data transfer, it arbitrates for the SCSI bus and, after
winning arbit ration, rec onnects to the initia tor and sends an IDENTIFY messag e via
the MES SAG E IN phase. This reviv es the I_ T _L ne xu s (initiat or-tar get- logi cal uni t
co nnec ti o n ) so th e initi ato r can r etri e v e th e co rre ct set of dat a p oin ters fo r the I/ O
process. The initiator restores the active pointers to their most recent saved values, and
the drive contin ues to finish th e origin al I/O process.
Disconnect-Reconnect is controlled with the Mode Select Command (15h) for the
Disconnec t/Reconne c t (02h) mode page.
The disk drive improves data throughput by skewing track and cylinder addresses.
W h e n the drive swi tche s he ads o r track s , or bo th , to a cces s se q uen ti a l data, the
rotation of the disk media allows one or more physical blocks to pass by the read/write
head before the head is re ady to continue the transfer. Skewing adjusts the block
addresses so that the head switch and settle times and the media rota tion coincide to
bring the head exactly to the next logical block. This minimizes rotational latency (and
increases throughput) when data is accessed sequentially.