[squid-users] about cache dirs

Hi all !!!
I am using squid 2.5stable4 and i am running 3 instances of squid on the
same box.
like this:
/usr/local/squid/sbin/squid -s -f /etc/squid.conf.1
/usr/local/squid/sbin/squid -s -f /etc/squid.conf.2
/usr/local/squid/sbin/squid -s -f /etc/squid.conf.3

each instance of squid has its own cache dir:
for example:
squid.conf.1 -> /var/cache1/ (1 gb)
squid.conf.2 -> /var/cache2/ (1gb)
squid.conf.3 -> /var/cache3/ (1gb)

my question for you is:
Can i use the same cache dir for the 3 instances, like this:
squid.conf.1 -> /var/cache/
squid.conf.2 -> /var/cache/
squid.conf.3 -> /var/cache/
 or each instance must have its own, not shared, cache dir ?

Thanks a lot

--
Diego