Fea tu re D es cri pt io ns
Maxtor Atlas 10K III 6-5
In any SCSI disk drive, bad blocks may be reallocated. However, a power failure or
unrecoverable data could threaten data integrity during a block reallocation.
The reallocation and defect list storage algorithms prevent a reallocation from being
lost due to a p ower fai l ur e. Once a real l oc a tion start s, the inf or mati on about the da ta
block to be moved is stored on t he media . As t he r eal loc ation progresses, checkpoint
information about t he reallocation (such as the new destination and the data in transit )
is recorded. If the reallocation is interrupted, the process can autom atically continue
from the last checkpoint without data loss.
If a block reall oc a tion is performed on unrecovera ble data (rare ), a Bad Data Mark is
set in the new location. Thus, there is no chance of undetected bad data being
generated from a reallocation.
Da ta can be verif ie d in tw o ways . Fi rs t, the i n te gri ty of data in s e l e cted a re a s of th e
media can be checked using the VERIFY command. Secondly, the WRITE AND
V E RIFY co m m a n d w ri te s host-s u pp l ie d da ta and then ve ri fi e s th a t i t was wri tten
correctly.
The Verify Error Recovery Page of the MODE SELECT COMMAND controls the
drive's response to error conditions that arise during the VERIFY command and
during the verify operation of the WRITE AND VERIFY command.
The drive supports all three SCSI-defined queue tag messages. When queuing is
enabled (default condition), the drive can accept any of the following:
•Simple - specifies that the command is to be placed in the drive's
command task set (queue). If several commands are pr esent, the drive
may reorder them to increase overall throughput.
•Head of Queue - directs the drive to place the com m and at the
beginning of the queue, to be executed next. Consecutive commands
with Head of Queue specified are executed in last-in-first-out (LIFO)
order. Queue depth is 64.
•Ordered - specifies that commands in the drive's task set are to be
executed in the order receive d (FIFO).
The DQue bit (disable queuing) of th e Control Mode page can be used to disable
tagged command queui ng.
The drive uses Optimized Reordering Command Algorithm (ORC A) and tagged
command queuing to provide greater throughput by reordering any commands
queued on the drive to minimize rotational latency, seek time and head selection time.
The performance improvem ent is significant in heavily loaded applications where
queue depth exceeds 10-15 commands.