I'm trying to upgrade our switch IOS. I used telnet to connect to the device, had setup the tftp server and started the service, the software was in the TFTP root, and typed copy tftp flash. The file copied over without an issue, but I never got the 'erase flash?' question. The current IOS running is in a sub-directory off the flash 'root'. Looking at a document 'Loading Cisco IOS Software', it's mentioned changing the config register to the value 0x2101. Why is that done? Is it necessary in each case?
Yes, if this is in production, do it during on outage window in case some thing goes wrong.
Also, take a look at the 3560 command reference guide to make sure every thing is correct before rebooting