Harddrive load cycles
I recently noticed a rather high “load cycle count” SMART value (“smartctl –all“) for my new harddrives that are only in operation for a few hours. Sure thing, I also heard the clicking noise of load-/unloading disk heads every now and then.
193 Load_Cycle_Count       0x0032  100  100  000   Old_age  Always      -      395
As the number of load cycles is somewhat limited – a rather high value, but limited nevertheless – over the lifetime of the disk I decided to disable the disk power management feature that caused these load cycles.
This can be done with the “hdparm” utility and the “-B” parameter:
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# hdparm -B /dev/sda /dev/sda: APM_level     = 128 # hdparm -B 254 /dev/sda /dev/sda: setting Advanced Power Management level to 0xfe (254) APM_level     = 254 |
Depending on disk firmware the APM feature is either disabled with a value setting of 255 or 254.
Note: This setting is usually lost after a power cycle, see below.
After setting the APM level the load cycle count stopped increasing – and also the clicking noises were gone.
In order to set this value on system boot I added the following to “/etc/hdparm.conf“:
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command_line { hdparm -q -B 254 /dev/sda } command_line { hdparm -q -B 254 /dev/sdb } |
In case you’re interested in the background of the low default APM value and the high load cycle count, as someone wrote on the linux-thinkpad mailing list:
Unloading heads is important for two reasons: unloaded heads are far less succeptible to damage due to sudden impacts to the drive, and allow for the linear head assembly positioning motor to be either turned off, or operated in reduced current.
So, it reduces idle power consumption of the drive, which is of paramount importance for the vendor’s marketing department since everyone overstates their battery longevity numbers. It can also decrease the chance of a damaged drive that needs to be returned in warrany on the cheap-o crap 1yr warranty service.
As my disks are getting written to quite often unloading the drive heads doesn’t make much sense and only wears out the drive head positioning/parking parts, therefore I prefer to disable this feature (for now).