UNIX fstab settings and prealloc command

[Brooks, Russ]

Hi,

  We're running online JFS on HP.  We had a recommendation given to us to replace the settings in fstab for the online redo logs and archive logs.  The settings were:

 

/dev/vgPRD03/lvPRDsaparch     /oracle/PRD/saparch    vxfs  delaylog   0       
/dev/vgPRD02/lvPRDoriglogB    /oracle/PRD/origlogB   vxfs  delaylog   0       
/dev/vgPRD01/lvPRDoriglogA    /oracle/PRD/origlogA   vxfs  delaylog   0       
/dev/vgPRD01/lvPRDmirrlogB    /oracle/PRD/mirrlogB   vxfs  delaylog   0       
/dev/vgPRD02/lvPRDmirrlogA    /oracle/PRD/mirrlogA   vxfs  delaylog   0

 

The recommended change would be:

 

/dev/vgPRD03/lvPRDsaparch     /oracle/PRD/saparch    vxfs  nodatainlog,convosync=direct   0       
/dev/vgPRD02/lvPRDoriglogB    /oracle/PRD/origlogB   vxfs  nodatainlog,convosync=direct   0       
/dev/vgPRD01/lvPRDoriglogA    /oracle/PRD/origlogA   vxfs  nodatainlog,convosync=direct   0       
/dev/vgPRD01/lvPRDmirrlogB    /oracle/PRD/mirrlogB   vxfs  nodatainlog,convosync=direct   0       
/dev/vgPRD02/lvPRDmirrlogA    /oracle/PRD/mirrlogA   vxfs  nodatainlog,convosync=direct   0       

 

What a different branch of the consultants gave us was:

 

/oracle/DV1/origlogA vxfs delaylog,convosync=direct  0 2
/oracle/DV1/origlogB vxfs delaylog,convosync=direct  0 2
/oracle/DV1/mirrlogA vxfs delaylog,convosync=direct  0 2
/oracle/DV1/mirrlogB vxfs delaylog,convosync=direct  0 2

 

They based this on a quick test using the following command:

 

/bin/time -p prealloc myfile 1000000000

 

which indicated a slight negative impact to I/O with the nodatainlog.  I've read the man pages on prealloc, but it isn't clear that this is a valid simulation of the online redo logs.  Does anyone have experience with this?  Was this a valid test?

 

Best regards,

Russ Brooks