What are you guys getting as a ratio for key_requests/key reads I cant seem to get this higher than 160, before I upped the key_buffer from 32Mb to 384Mb it was only 100 the with 384Mb it was about 160 I have now upped it to 512Mb and its still 160.

In that tuning artical on one of the other posts it hint at this figure being over 1000 !

My info:
Key_read_requests 53846996
Key_reads 341678
key_buffer_size 536866816

is there a way I can see the what the highest use of the 512mb has been ? I can work out an averge using the uptime but cant see a max figure.

You can find out the usage of you Key Buffer with the following:

Cache Miss Rate = Key_reads / Key_reads_requests

The Cache Miss Rate should be smaller than 0.01.
I think with your 0.006 you are good.

The usage of your Key Buffer is shown in the Key blocks used value in the output of SHOW STATUS

So long...

Indy

Edit: You can use the Cache Miss Rate for finding an optimal size for your Key Buffer. Decrement the size and let MySQL run for while. Then take a look again, if the CMR is not higher, then the smaller size will be ok.