df command in hang state on AIX two node cluster .

df command in hang state on AIX node

Incident:

on AIX two node hacmp cluster ,when we executed df -gt command , in command output observed that some nfs mount was missing and command is not exiting and in hang state.
because of this TSM backup for AIX node was failing.

Analysis:
After analysis found that one filer mount is missing on server and AIX cluster node was trying to mount it.we checked nmon log file and also /etc/filesystems to find missing mount entry.

solution :

forcefully umounted that filer and after that df -gt works and also TSM backup also worked
after that requested filer access to storage team which was not accessible.

umount -f /nfs-mountpoint  and then TSM backup and df -gt also working fine.

After doing analysis of df -gt hang issue we also found that at Firewall level there was rule missing for communication between AIX server and filer ,so to resolve  issue at network level Firewall rule need to be implement and need to mount again to solve this issue.

df command may hang on AIX NFS clinet when NFS server is down or crashed from where file-system exported to client.

Also want to discuss on mount type in AIX.there are two types of mount 
1.HARD
2.SOFT

so here question is which one is better .As per my knowledge and experience soft mount is the best option while doing NFS mount. generally these two parameter define that if there is nfs mount crash or mount point is not accessible then how nfs client react.

why soft mount is better ??

 AIX node tries until timeout value reach ,but in hard mount it there is no  timeout value defined so AIX server try indefinitely ,so in this situation system performance may degrade.


Thanks !!!!!!