Describe the fragmentation metric in zpool.8

[behlendorf]

While it's commonly understood that a larger fragmentation value
is worse than a smaller one it is never explained anywhere but
the source what this value means. Using the comment in the source
add this information to the zpool.8 man page.

Signed-off-by: Brian Behlendorf behlendorf1@llnl.gov

[behlendorf]

I'm all for a better description of the fragmentation metric if someone wants to write it. As you point out this text does actually just describe a single metaslab. But after being asked this question at least half a dozen times I wanted to add something to the man page and grabbing the text from the code was easy. Better descriptions welcome!

[dweeezil]

Indeed, the number is there and I'm quite certain everyone wants to know what it means. I'll give a shot at writing some text to glue the various layers together.

[behlendorf]

Closing. We can wait for some better text.