A hybrid disk drive, i.e., a disk drive with two types of permanent
storage media (conventional disk media and nonvolatile memory, such as
flash memory), uses its nonvolatile memory in operational modes other
than the power-save or "standby" mode wherein the disks are spun down. In
a first additional mode, called a "performance" mode, one or more blocks
of write data are destaged from volatile memory (the disk drive's write
cache) and written to the disk and simultaneously one or more data blocks
of write data are destaged from the volatile memory and written to the
nonvolatile memory. In a second additional mode, called a
"harsh-environment" mode, the disk drive includes one or more
environmental sensors, such as temperature and humidity sensors, and the
nonvolatile memory temporarily replaces the disks as the permanent
storage media. In a third additional mode, called a "write-inhibit" mode,
the disk drive includes one or more write-inhibit detectors, such as a
shock sensor for detecting disturbances and vibrations to the disk drive.
In write-inhibit mode, if the write-inhibit signal is on then the write
data is written from the volatile memory to the nonvolatile memory
instead of to the disks.