NFS server export file content
more /etc/exports /opt/backup 192.168.0.66(rw,sync,all_squash,insecure,anonuid=500,anongid=500)anonuid and anongid represent user id and group id of oracle user on NFS client (server running the DB). no_root_squash has not been used.
Options used for mounting the NFS are
1. mount -t nfs -o rw,hard,rsize=32768,wsize=32768,vers=3,nointr,timeo=600,tcp,nolock 192.168.0.76:/opt/backup /opt/backup (backup time : 06:45)
2. mount -t nfs 192.168.0.76:/opt/backup /opt/backup (backup time : 07:05)
3. mount -t nfs -o rw,hard,rsize=32768,wsize=32768,vers=3,nointr,timeo=600,tcp,nolock,actimeo=0 192.168.0.76:/opt/backup /opt/backup (backup time : 06:35)
In test 1 the mount is without actimeo. Test 2 doesn't specify any mount options and rely on default options. In test 3 the options are similar to test 1 with the exception of actimeo being included.
There's some confusion as to when to use actimeo option. Some documents state it explicitly not to use noac option RMAN but say nothing explicitly about actimeo option but at the same time states it could be used with single instance databases (359515.1) while others explicitly state not to use actimeo with single instance and only required to RAC (1164673.1,762374.1). Neverthless the option 3 was able to complete the backup in roughly same time at option. However use of noac increased the backup time unacceptably long (into hours. Not included in the post).
Below is the IO rate and throughput observed from the emconsole during each test.
Useful metalink note
Howto Optimize NFS Performance with NFS options. [ID 397194.1]
How To Setup DNFS (Direct NFS) On Oracle Release 11.2 [ID 1452614.1]
Step by Step - Configure Direct NFS Client (DNFS) on Linux (11g) [ID 762374.1]
Mount Options for Oracle files when used with NFS on NAS devices [ID 359515.1]
NFS Performance Decline Introduced by Mount Option "actimeo=0" [ID 1164673.1]