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XL500S
errors. The procedure ends when error recovery is achieved or when all possible retries have
been attempted.
Extended Read Retry Procedure – This retry procedure tries combinations of positive/negative
track offsets and data DAC manipulations to recover the data. This retry procedure applies
only to read data recovery. The Read/Write Retry procedure performs the actual retry
operation.
When an extended retry operation is successful, the controller continues with the command.
The controller clears any changes in track offset or data DAC settings before the command
continues.
3.11
Hot Plug Support
SATA supports hot plugging (also known as "hot swapping"), the ability to swap out a failed
hard drive without having to power down the system or reboot. This capability contributes to
both data availability and serviceability without any associated downtime, making it a critical
feature for extending SATA into enterprise applications.
The drive supports hot plugging only in systems where a SATA hard drive storage backplane
is used.
The Serial ATA revision 2.5 specification requires staggered pins for both the hard drive and
drive receptacles. Staggered pins mate the power signals in the appropriate sequences
required for powering up the hot plugged device. These pins are also specified to handle in
excess of the maximum allowed inrush current that occurs during drive insertion. SATA-
compliant devices thus need no further modification to be hot pluggable and provide the
necessary building blocks for a robust hot plug solution, which typically includes:
Device detection even with power downed receptacles (typical of server applications).
Pre-charging resistors to passively limit inrush current during drive insertion.
Hot plug controllers to actively limit inrush current during drive insertion.
3.11.1 Hot Plug Technical Issues
Reliable hot plugging of disk drives requires careful design of specific issues. Generally, hot
plugging is only allowed when blind mating with a backplane, where there are controlled
tolerances for alignment of mating connectors. The main issue is preventing droop (a
momentary drop in voltage) of the backplane's voltage busses during insertion because of
inrush current to charging bypass capacitors in the disk drive.
3.11.1.1 Methods of Controlling Inrush Current
There are two methods of limiting inrush current when hot plugging disk drives. They are hot
plug controller IC's and precharge resistors.
3.11.1.1.1 Hot Plug Controller IC's
Hot plug controller IC's ramp up voltages to the inserted disk drive at a controlled slow rate (a
constant dv/dt), after full connector mating has been established. This eliminates almost all
inrush current. This method does not require staggered precharge contacts, although there
usually is a staggered ground 'mate first' pin(s) to ensure ground connection before making
power and signal connections. Sometimes added ground pins on both ends of the mating
connector are staggered 'mate last' providing the hot plug controller a clear indication of all
other pins making solid contact. From an engineering standpoint, this is the most reliable
method of hot plugging disk drives, but is expensive to implement on backplanes.
2679-701211-A06
RELEASED 10/21/10 (WD CONFIDENTIAL)
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