Hi, Just wanted to throw some analysis into this bug report. It's take
me ~30+ hours of running tests to gather this data, so apologies if this
comes late in the day once the fix has been committed :-/

I've measured Spin Start/Stop counts on a HP Mini netbook measuring the
start/stop count during 30 minutes of idle time for various settings of
the spindown time.   I ran these tests for hdparm -B 127 and also hdparm
-B 128, and each test was ran twice to calculate an average and
std.deviation.   I also used a precision 6 digit multimeter and measured
power consumption for each run to measure the impact of the various
spindown times.

Attached is an LibreOffice spreadsheet with the data and some graphs.

No big surprises in the data - as the spintime increases we reduce the
number of start/stops over the 30 minute idle time and also we see power
consumption increasing since we are using more power to keep the drive
spinning.   The interesting thing to take from the data is the fact that
the power savings between 60 seconds spindown time and 600 seconds are
~10-15 mA which is about ~3% of the total power consumption.   So
probably a good compromise is ~2-3 minutes spindown time for an idle
system.

I'd like to repeat this with a more modern laptop and larger HDD, but
alas my x220i is away for repair this week.


** Attachment added: "hdparm spindown time analysis"
   
https://bugs.launchpad.net/ubuntu/+source/hdparm/+bug/952556/+attachment/2930971/+files/hdparm-spin-time-analysis.ods

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Title:
  [Precise] [Hardware-killer] HD restarts every few seconds

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