sleeping the hard drive

what does linux consider `idle` regarding hard disk activity? i`m trying to set hdparm to put to sleep my hd after 30 minutes of inactivity `hdparm -S 241 /dev/hda2`, but the drive simply refuses to.
is it because i have set cron jobs? or is it some of the processes, like kflushd, /sbin/update, or kswapd that keep the hd from resting?
thanks in advance, specially from my hd...
all the commands were executed as root, and the machine is not used as a server or any other type of task, is a humble 486 `monouser`, once i log out nobody uses it. the lilo instruction `no_hlt` is not set.
system info: slackware 4.0.0/linux 2.2.6/486 [Checking 'hlt' instruction... OK.]

Hictio, my response would be that your hardware doesn't support that functionality, although the software does. You have to remember that the 486, from a hardware point of view, is a rather tame beast, not supporting the capabilities of the newer pentium and above class machines. -mk

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If it ain't broke, fix it till it is.

thanks, mike; that`s too bad... i guess you`re right, in term of `computing years`, that machine is something close to a pterodactyl...
thank you very muchm, tho, let you know if i came up with something.