Ultrastar 7K2
HGST Hard Disk Drive Technical Reference Manual
21
SATA 6 Gb/s
SATA 6 Gb/s is the next generation interface for SATA hard drives. It adds to the functionality of the
SATA 3 Gb/s interface with the following features:
Native Command Queuing (NCQ)
— server feature for performance in random I/O transaction
environments. It aggregates many small random data transfers and allows the disk to reorder the
commands in a sequential order for faster access.
Staggered Spin-up
— allows the system to control whether the drive will spin up immediately or
wait until the interface is fully ready before spinning up.
Asynchronous Signal Recovery (ASR)
— robustness feature that improves signal recovery.
Enclosure Services
— defines external enclosure management and support features.
Backplane Interconnect
— defines how to lay out signal line traces in a backplane.
Auto-activate DMA
— provides increased command efficiency through automated activation of the
DMA controller.
Time-Limited Error Recovery (TLER)
HGST has delivered coordinated error management in the form of Time Limited Error Recovery (TLER).
TLER-capable hard drives will perform the normal error recovery and, after 7 seconds, issue an error
message to the RAID controller and defer the error recovery task until a later time. With coordinated error
handling, the hard drive is not dropped from the RAID array, thereby avoiding the entire RAID recovery,
replacement, rebuild, and return experience.
The error handling is further coordinated between the TLER-capable hard drive and the RAID card. The
TLER capable drive will respond without waiting on the error to be resolved. RAID cards are very capable
of handling this with a combination of parity protection and journaling. The RAID card flags the error in the
error log and proceeds to deliver data using parity protection until the drive retries its own error recovery
and corrects the error. This is quite similar to error management proven in SCSI- RAID for many years.
Though TLER is designed for RAID environments, it is fully compatible with and will not be detrimental
when used in non-RAID environments.
