Technical information

HGST Ultrastar C15K600 Hard Disk Drive Specification
148
command determines which seek counter is incremented. The Zero Seek counter is incremented if a seek is not
required or if only a head switch is required to access the first Logical Block. After the initial seek, no further counter
incrementing is performed for that command.
Note: The length of a seek as reported in page 30 may differ from expected results. The reason for this is that
the drive executes Idle Time Functions between operations of the drive. The seek operations that occur in Idle Time
Functions are not directly entered into page 30 seek counters but they change the length of the following seek. This
is because after the Idle Time Function is completed, the heads will not necessarily be in the same position as they
were at the completion of the previous command.
A buffer overrun or under run condition occurs when the Initiator does not transfer data to or from the Target data
buffer fast enough to keep up with reading or writing the media. The buffer overrun counter is incremented during
operations that require a Data In phase when a buffer full condition prevents the continued transfer of data from the
media to the data buffer. The buffer under run counter is incremented during operations that require a Data Out
phase when a buffer empty condition prevents the start or continuation of a data transfer from the data buffer to the
media (or a data transfer from the media for a Verify command with BytChk=1).
Buffer Overrun conditions are detected during the following SCSI commands:
- READ (6)
- READ (10)
Buffer Under Run conditions are detected during the following SCSI commands:
- VERIFY WITH BytChk=1
- VERIFY (16) WITH BytChk=1
- WRITE (6)
- WRITE (10)
- WRITE AND VERIFY
- WRITE AND VERIFY (16)
- WRITE SAME
- WRITE SAME (16)
- ZERO SEEKS
The number of times no seek was required. The operation may have resulted in a head switch.
- SEEKS >= 2/3 DISK
The number of seeks equal to or greater than 2/3 of the disk.
- SEEKS >= 1/3 AND < 2/3 DISK
The number of seeks equal to or greater than 1/3 and less than 2/3 of the disk.
- SEEKS >= 1/6 AND < 1/3 DISK
The number of seeks equal to or greater than 1/6 and less than 1/3 of the disk.
- SEEKS >= 1/12 AND < 1/6 DISK
The number of seeks equal to or greater than 1/12 and less than 1/6 of the disk.
- SEEKS > 0 AND < 1/12 DISK
The number of seeks less than 1/12 of the disk.
- OVERRUN COUNTER
The number of times that data was available to be transferred from the media but the device buffer still
contained data that had not been retrieved by the Initiator. Consequently, the disk had to take additional
revolutions until the buffer was available to accept data.
- UNDER RUN COUNTER
The number of times that the drive was ready to transfer data to its disk (on a write), but its buffer was empty
(i.e., had not been filled by the Initiator), thus the disk was forced to take extra revolutions.