Messages in this thread |  | | | Date | Mon, 31 Jul 2000 18:40:48 +0200 | | From | Matthias Andree <> | | Subject | Re: (reiserfs) Re: sync: why disk cannot spin down |
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On Mon, 31 Jul 2000, Marc Lehmann wrote:
> On Mon, Jul 31, 2000 at 04:53:00PM +0200, Matthias Andree <matthias.andree@gmx.de> wrote: > > My point is: putting a drive to sleep rather than to standby will not > > help much, it will only delay the spin-up and possibly leave you with a > > slower drive. > > Cool logic. How do you define "much"? Drive electronics can still use > a lot of power, and most users (xuan and me excluded ;) want this for > power-save.
How much you get, depends on how much the actual drive saves. Still, you lose performance, you possibly lose the settings, that's on the negative side. I'm aware of these implications, a good friend of mine has written his diploma thesis in electrical engineering on exactly this topic, namely "Algorithmen für den leistungsarmen Betrieb mobiler Festplatten" (German-language, translates to 'algorithms for the low-power operation of mobile hard disk drives'). Contact me in private mail if you need more information.
He collected some information from manufacturers that I'm working up here: (quoting from
manuf.+model IBM DARA Hitachi Fujitsu Seagate Ma- Maxtor cont'd 225000 DK22AA 2064AT rathon 2250 251010A
power (W) active 2.6 2.22 2.15 2.50 1.83 idle 2.0/1.3/0.85 1.7/0.8 0.95 1.20 0.90 standby 0.25 0.25 0.35 0.30 0.20 sleep 0.1 0.125 0.13 0.10 0.10
So, effectively, you gain about 100..200 mW by putting a drive from standby to sleep, while you gain roughly 1000 mW from idle to standby after gaining 0.5 .. 1.5 W from active to idle. (depends on the usage pattern). OTOH, if you're talking about power, the more interesting thing is the energy (integral t0...t1 P(t) dt), and waking up electronics and spinning up the drive costs additional energy, even if it's only for the delay until the request is satisfied. If waking up from sleep costs additional seconds, that's going to cost battery life, to put it popularly.
> In practise, of course, there is a clear trade-off between ugly error (!) > messages from the kernel drawing for your attention and not putting the > drive to sleep.
The error message is natural, a drive put to sleep is put there permanently, since the drive is supposed to power down its interface electronics as well.
> In general, the kernel support is lacking much with respect to > power-savings (just spin down your scsi-drive to get some nice hang (and > yes, I know the scsi-idle patch)).
Since SCSI drives are only manually powered down, the Kernel is fine in this respect, although it leaves room for feature requests, admittedly :-)
-- Matthias Andree
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