direct I/O with VxFS

[KC]

Dear list,   Our shop is running Solaris 2.6, Oracle database 8.0.6 and Veritas VxFS file system. At present, all database file access thru the file system buffer cache, we decided to use the direct I/O mount option with VxFS for performance reason. There is one issue I am not sure about and hope someone on the list can give me a pointer, access database file thu the file system buffer cache gives us "read ahead" advantage, with direct I/O I think what you read is what you get (no read ahead functionality), is this an issue?? If it is an issue, how do you deal with it?? WIth file system buffer cache, I think  the database block size should be the same as file system buffer size and file system block size is irrelevant to how much system read or write, is this still true under direct I/O, I am not sure what dictate how much data to read or write??   KC