Re: .ini settings for ADD KEY to 30Gb table on 96Gb machine?

[Rick James]

So, you will end up with 330GB of data and 400GB of indexes in your 11 MyISAM tables?

Will you be hitting more than one table at a time?

It might be cheaper and faster to get a large SSD drive(s) rather than use such a huge (but not big enough) RAM. (Virident is among the fastest.)

Extra CPUs won't help much. (Alas, this is a deficiency in the MySQL code.)

Adding index(es) to a MyISAM table either
* Uses key_buffer (and does lots of I/O for a table of your size)
* Does a unix sort (usually much faster)
It is hard to trick it into doing the latter.
This may explain the radically different times you experienced.