cpu load on new filesystem

We've moved an oracle install to a new server. The server is a V490 and identical to the server it was on previously, except now the filesystem that contains the oracle datafiles and logs is on vxfs/san, as oppose to the previous ufs/scsi array.

The system isn't complaining about io, but the cpu load has doubled, prstat shows cpu load constantly around 5, wheres before it would be around 2/3.

We can't understand why the cpu load would increase, any thoughts of what to check ? We know the vxfs block size is only 1k when the ufs block size and oracle block size are 8k, would this make a significant difference ?

Cheers

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Michael