When is it safe to disable InnoDB doublewrite buffering?
The only situation I can think of is reloading a large mysqldump. Why ?

Check out this Pictorial Representation of InnoDB (Percona CTO Vadim Tkachenko)



From the picture, you can see that the InnoDB Buffer Pool writes dirty pages to


Log Buffer
Insert Buffer in ibdata1
Double Write Buffer in ibdata1
.ibd file for each InnoDB table


Shutting off the Double Write Buffer will let a mysqldump write data and index pages in the tables faster since it does not have to write the same 16K pages to ibdata1. 

Production Servers should never have the Double Write Buffer disabled. If you do so for loading data faster (during maintenance of course), enable it immediately after reloading the DB Server.

In other words,


Add innodb_doublewrite = 0 to my.cnf
Run SET GLOBAL innodb_fast_shutdown = 0;
Restart mysql
Load mysqldump
Remove innodb_doublewrite = 0 from my.cnf
Run SET GLOBAL innodb_fast_shutdown = 0;
Restart mysql