Hi Masaru-san,
Not sure what do you mean by SDU - probably not SnapDrive for UNIX?
This is a very good doc explaining SMMOSS 5.0 workflow:
https://fieldportal.netapp.com/ci_getfile.asp?method=1&uid=7178&docid=24326
Comments below slide 25 describe in detail a process of backing up Search Indexes. Basically SharePoint services get paused (hence the need for an agent), LUN with indexes is snapped via SDW & then SharePoint services are restarted.
Regards,
Radek