[Ukfreebsd] "green" HDDs
frank at shute.org.uk
Wed Jan 12 08:36:37 GMT 2011
On Tue, Jan 11, 2011 at 01:15:26PM +0000, Tim Borgeaud wrote:
> Despite the fact that green credentials of these drives may be
> questionable, I think that in typical usage there are some definite
> As far as I can tell, the performance of the somewhat slower spinning
> (5400 rpm) drives is not really that terrible at all. I believe that the
> slower spinning drives compare poorly in terms of random access, but
> overall there isn't a huge difference (at least not between similarly
> priced drives).
If the disk is parked, then I can imagine that reads or writes are
going to be slow; I'm assuming that it has to be run up to full speed
before it can be written too.
> I suspect that the very aggressive power management features won't make
> any significant difference other than giving the drive a particular set of
> statistics with which it can be compared to others. However, I also
> suspect that in the vast majority of cases, drives will be idle for
> virtually the entire time that the host computer is turned on. I,
> therefore, think that any additional power and strain caused by waking
> from any power saving state is likely to be negligible.
I think it depends on whether the machine it is in is tasked as a
server or a desktop. My webserver gets a hit every 5 mins or so, so if
it's not cached then it's going to be spun up.
> Where the drives may have some advantage is where is it useful to keep the
> overall power of a system low. This may be for battery powered devices or
> it may be to allow a compact or very quiet computer. It's probably also
> worth noting that it is often the case that the slower spinning drives are
> also slightly quieter than the faster drives.
I can see them being of some use in laptops, like you say.
I did once emulate one of these disks with my laptop and Linux. I
disabled fsync() from being called so often by periodic (I think) and
tuned the HDD with hdparm to spin down after x mins of inactivity. It
was about 10 yrs ago so the details maybe sketchy/wrong.
It worked OK but then I was only using an editor away from the mains.
Latency was horrible. I've no idea how long it extended battery life
by, as I never tested it.
> I also suspect that there may actually be some small benefit in power
> savings when considering large quantities of such drives in situations
> where the idle power of systems is relatively low (where a watt or two per
> drive might actually make a difference).
As you say, a server farm or similar might be a possibility but you'd
have to work round the latency.
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