WDEPC

Western Digital EPC(Extended Power Condition) control tools for Linux.

This tool is only tested on Western Digital HC320 disk, but may work in other Western Digital disk supported EPC.

All query function is 99% safe, unless your disk translate those command into some wrong WRITE command.

USE AT YOUR RISK.

What is EPC (Extended Power Condition)

APM - Advanced Power Management

There was a power management mechanism called APM - Advanced Power Management in the late 90s.

It is supported by almost all hard drives.

APM defines a APM Levels from 0 - 255.

level	description
0	Reserved
1	Minimum power consumption with Standby
2 - 127	Intermediate power management levels with Standby
128	Minimum power consumption without Standby
129 - 254	Intermediate power management levels without Standby
254	Maximum performance
255	Reserved

where standby means spin down.

EPC - Extended Power Condition

This is the latest power management standard in hard drives, it's usually supported on enterprise-grade hard drives (some newer hard drives don't support APM, EPC is used exclusively).

EPC defines two main state:

1. PM1: Idle state
   1. Idle_a: drive ready, not performing I/O; drive may power down some eletronics to reduce power without increasing response time.
   2. Idle_b: spindle rotation at 7200 with heads unloaded.
   3. Idle_c: spindle rotation at low RPM with heads unloaded.
2. PM2: Standby state
   1. Standby_y: same as Idle_c in Seagate and WD
   2. Standby_Z: Actuator is unloaded and spindle motor is stopped. Commands can be received immediately.

a SATA state sleep, same as Standby_z but require soft reset or hard reset to return to mode Standby_Z.

Current tools like hdparm can not update EPC settings like timer, enable or disable, so this tool came up.

Usage

Check Power Mode

get current power mode

wdepc -d /dev/sda check

Output:

idle a

Enable EPC

Enable EPC and disable APM.

The APM is disabled automatically and can not be controlled.

wdepc -d /dev/sda enable

Disable EPC

Disable EPC, but doesn't re-enable APM.

You must enable APM MANUALLY on demand.

wdepc -d /dev/sda disable

Show EPC settings

Show EPC settings, include timer, state

wdepc -d /dev/sda info

Output:

* = enabled
All times are in 100 milliseconds

Name       Current Timer Default Timer Saved Timer Recovery Time Changeable Savable
Idle A     *20           *20           *20         1             true       true
Idle B     *6000         *6000         *6000       10            true       true
Idle C     0             0             0           40            true       true
Standby Y  0             0             0           40            true       true
Standby Z  0             0             0           150           true       true

Force device goto a state

wdepc -d /dev/sda set <idle_a | idle_b | idle_c | standby_y | standby_z >

Set timer

Set specific mode timer.

wdepc -d /dev/sda set-timer <mode> <timer> --save --enable true

If --save present, save the timer setting even after reboot.

--enable controls if the timer is enabled.

Set state

Enable or disable a specific mode.

wdepc -d /dev/sda set-state <mode> --save --enable true

If --save present, save the state setting even after reboot.

--enable controls if the power state is enabled.

Restore settings

Restore a specific power mode setting.

wdepc -d /dev/sda restore -d -s <mode>

If --default present, set current setting to default, else set current setting to saved setting.

If --save present, save current setting.

Reference

1. HC320 SATA spec
2. https://serverfault.com/a/1047332
3. Seagate SCSI Reference