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hwmon: (drivetemp) Add usage not describing impact on drive spin-down

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On some drives, reading the drive temperature resets the drive's
spin-down timer. If the drive temperature is read too often, affected
drives will never spin down. Add this information as usage note to
the driver documentation.

Reported-by: Peter Sulyok <peter@sulyok.net>
Cc: Peter Sulyok <peter@sulyok.net>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
This commit is contained in:
Guenter Roeck 2020-08-08 18:07:10 -07:00
parent 787c095eda
commit e403583909
1 changed files with 18 additions and 0 deletions
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18
Documentation/hwmon/drivetemp.rst
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@ -30,6 +30,24 @@ Transport is not supported, the driver uses SMART attributes to read
the drive temperature.
Usage Note
----------
Reading the drive temperature may reset the spin down timer on some drives.
This has been observed with WD120EFAX drives, but may be seen with other
drives as well. The same behavior is observed if the 'hdtemp' or 'smartd'
tools are used to access the drive.
With the WD120EFAX drive, reading the drive temperature using the drivetemp
driver is still possible _after_ it transitioned to standby mode, and
reading the drive temperature in this mode will not cause the drive to
change its mode (meaning the drive will not spin up). It is unknown if other
drives experience similar behavior.
A known workaround for WD120EFAX drives is to read the drive temperature at
intervals larger than twice the spin-down time. Otherwise affected drives
will never spin down.
Sysfs entries
-------------