[Linux-cluster] Behavior of "statfs_fast" settune

[Wendy Cheng]

>
> For GFS1, we can't change disk layout so we borrow the "license" file 
> that happens to be an unused on-disk GFS1 file. There is only one per 
> file system, comparing to GFS2 that uses N+1 files (N is the number of 
> nodes in this cluster) to handle the "df" statistics. Every node keeps 
> its changes in memory buffer and syncs its local changes to the master 
> (license) file every 30 seconds. Upon unclean shutdown (or crash), the 
> local changes in the memory buffer will be lost. To re-sync the 
> correct statistics, we need to use real "df" command (that scans the 
> on-disk RGRP disk structures) to adjust the correct statistics. For 
> details, check out one of my old write-ups in:
>
> http://people.redhat.com/wcheng/Patches/GFS/readme.gfs_fast_statfs.R4
>

BTW, I'm not very happy with this implementation and there are few other 
ideas on the table. However, since GFS2 is imminent (I hope), will keep 
the code as it is today. 

-- Wendy