acpi S4 resume partition

[toxa]

Sorry for stupid question but I can't find good documentation about
preparing system for hibernating with acpi.
I mean, if I use acpiconf -s4 (suspend to disk) then system should to put
all memory contest info physical partition and resume from it when booting
by bootloader, shouldn't it? So I have to prepare such partition and tell
system (probably using loader.conf) to use it for hibernating. Something
like "resume=/dev/hda2" in lilo.conf in linux. Am I right? Because for now
acpiconf -s4 puts my system into shutdown/sleep, and, when I powering on, it
boots into new session, with "partitions was unproperly unmounted" errors.