If please relevant docs.
The concept is very simple.
SLP makes a number of duplications, but until the duplication is made the original backup will never be deleted.
Best practice guide
White paper on SLP
Thanks for your info ,explain me and give me the doc so that i can understand and i need doc for Netbackup 7.1 and above (7.5)
SLP was introduced in 6.5. The White Paper explains the concepts that are relevant to all versions, including 7.1 and 7.5.
TECH153154 Best practices for using Storage Lifecycle Policies and Auto Image Replication in NetBackup 7.1 is for 7.1 and 7.5.
You can also read up about SLP in chapter 14 of Admin Guide I :
NBU 7.5 Administrator's Guide for UNIX and Linux, Volume I http://www.symantec.com/docs/DOC5157
Supporting Storage Foundation and VCS on Unix and Windows as well as NetBackup on Unix and Windows
Handy NBU Links