3.8. Aggressive Link Power Management
This mode sets the link to its lowest power state (SLUMBER) when there is no I/O on the disk. This mode is useful for times when an extended period of idle time is expected.
This mode sets the link to the second lowest power state (PARTIAL) when there is no I/O on the disk. This mode is designed to allow transitions in link power states (for example during times of intermittent heavy I/O and idle I/O) with as small impact on performance as possible.
medium_powermode allows the link to transition between PARTIAL and fully-powered (that is "ACTIVE") states, depending on the load. Note that it is not possible to transition a link directly from PARTIAL to SLUMBER and back; in this case, either power state cannot transition to the other without transitioning through the ACTIVE state first.
ALPM is disabled; the link does not enter any low-power state when there is no I/O on the disk.
/sys/class/scsi_host/host*/link_power_management_policyexists. To change the settings simply write the values described in this section to these files or display the files to check for the current setting.