We have just completed our upgrade to V2R1 this past weekend (13+ hours a SAVSYS) and thought we had straightened out all the bugs. Then we ran our first weekly backup (SAVLIB *NONSYS). This backup normally takes 3 1/2 to 4 hours to complete; however, this time it took over 7 hours (nearly twice as long as normal). After scanning some inquiries in IBMLINK, I found the answer to the problem.
Apparently many of the system objects on the system were still compressed and the first time a compressed object is used (i.e., saved) it must be decompressed. This extended time for the SAVLIB *NONSYS should occur only on the first save after the install. The only mention about compressed objects and performance degradation in the installation documentation was in the Memo to Users (3.18). IBM did not highlight or warn about the effect on save commands. In hindsight, I would have either done a SAVLIB *NONSYS immediately after the install or made sure there was enough free storage on the system to allow the install to decompress all the system objects.