Red Hat

but i am using centos 6

i dont know exactly about -S means ,but a helpful info i am pasting please explore more
on this

Recording disk statistics with sysstat on RHEL/CentOS


Unlike on Debian-like systems, the default configuration for sysstat’s sa1 collector on RHEL/CentOS does not include disk statistics (like you would get from iostat) in the sa collection output. This is due to a missing flag in the cron.d fragment that calls sa1. The “-A” flag to sa1 defies reasonable assumption about its function, and does not include disk statistics, so we have to specify “-d” manually.

To enable disk statistics collection/trending, edit /etc/cron.d/sysstat and change the following:

*/10 * * * * root /usr/lib64/sa/sa1 1 1

to this:

*/10 * * * * root /usr/lib64/sa/sa1 -d 1 1

(Obviously, replace “lib64″ with “lib” as appropriate for i386 systems.)

Either wait for the next sa log rotation (at midnight) for sa1 to begin collecting disk statistics, or delete your current day’s statistics. sa1, for whatever historical reason, does not add new counters to an existing sa log file.

Thanx venkatareddy.
i googled it for some time, and i got info about everything else except "-S DISK"....