Today I had my MBP 1.83 sitting idle on a table in a quiet room. Because it was so quiet I could hear the HD spinning and that was the only detectable noise (besides the f_ing processor whine..).
I noted that the screen saver came on, the screen then went to sleep, but still the HD kept spinning and spinning and never stopped. Then I realized I wasn't sure if I'd ever heard the HD spin down/up so I did some tests....
Configuration:
-MBP 1.83, 1.5 GB RAM, 10.4.7
-No applications running except Activity Monitor (850+ MB RAM free)
-Airport & Bluetooth OFF, no networking of any kind
-No external devices of any kind
-Energy Preferences set to preconfigured "Normal" - allows HD sleep
-Plugged in and on battery, symptom is same
-Logging in and out and repeating, symptom is same
Symptom:
-HD never spins down despite no user activity of any kind
-Observed on and off power adapter for 40+ mins
Causes:
-Isolated, intermitent page-outs (called writes out/sec in Activity Monitor) prevent disk spin-down
-Page-outs are usually single (1 writes out/sec) and occur at 16.25 KB/s at approx. 1-2 min. spacing
-Multiple page-outs also occur (e.g., 16 writes out/sec), but more rarely than singles
-Page-ins were not observed
Effects?:
-Significantly decreased battery life when doing non-disk intensive tasks?
-Unnecessary heat generation?
Discussion:
Page-outs do nothing more than take data in physical RAM and put it into virtual memory. This is a good thing if the system is active and RAM needs to be allocated to active processes. However, if over 800 MB of RAM are free on a completely idle system, then it is unclear to me why the OS would allow intermitent single pageouts at the expense of HD sleep.
If this issue is not isolated, I think that it could be rather serious when it comes to energy management and portable battery life. Significant power savings occur if the HD can be powered down. If something intrinsic about memory management in OS X is preventing that, it needs to be fixed ASAP.
If someone could verify this behavior I would appreciate it.
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