Compressing unix disks

[Doug Mckenzie]

>Doing a 'df' shows that the system reserves 10% of each partition, since
>the amounts in the used and available columns only add up to 90% of the
>total blocks in each partition.  My boss maintains that 10% of the
>AVAILABLE blocks must be kept free, leaving us with only about 81% of the
>total disk space.  I think that the system's already got the space it needs.
>
>Could someone PLEASE tell me I'm right, so we can get back all that wasted
>space?  (9% of 3 Fuji Eagles)

Using 90% of the (total) disk blocks is a good tradeoff between disk
space and block allocation.  That's why it's the default (on HP's HP-UX).
The idea is: if there's lots of free disk space, you can get the block
you ask for, as less and less space is available, you have to go through
ever more brute search methods to find a block.  At 90%, search by hashing
cylinder group numbers and finally linear searching start to predominate. 

mck