I have a old bind dns server (linux centos5.5 with bind 9.3.6) with 2000+ zone files. Whenever any change is done in any file the dns is restarted. I guess a reload must be sufficient though.

Problem is that a restart takes a long time 50s-60s and dns requests fail during that time. 

This must be a very common issue , What is the correct way of restarting bind