Just an update on this old topic for anyone that's interested - here is the answer I got from IBM: "We don't use cio for archive logs because it technically isn't supported - i.e. Oracle isn't "cio aware" in it's treatment of archive logs. Online redo logs are written in multiples of 512 bytes, not 4096 bytes. We cannot tell you what the range of I/O transfer size possibilities is for archive logs because Oracle does not publish this information. If you force a log switch, presumably you are writing only the relevant portion on an online redo log, so it's probably reasonable to assume that AT LEAST the final I/O is likely not to meet the CIO requirements if the filesystem has agblksize=4096. If Oracle were to make public support statement that all archive log reads are writes are in 4k increments and are on 4k boundaries, we could certainly revisit our position. We would certainly recommend 'rbrw'" I also found the same recommendation here (http://unix.ittoolbox.com/groups/technical-functional/ibm-aix-l/direct-io-and-concurrent-io-in-oracle-1304545) and he also gives another reason for not using cio/dio for the archive logs - because the buffer cache can provide faster reads, which can speed up recovery. Regards, Brandon -----Original Message----- From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of Allen, Brandon Sent: Thursday, May 27, 2010 10:26 AM I received a response from Oracle in my SR and they said that the only reason they recommend not to put archive logs on a CIO file system is because that's what IBM recommends and they suggested I ask IBM for further explanation. They also referred me to the below presentation from IBM, which says on slide 18 "Archive Logs - Do not use DIO or CIO", but unfortunately again gives no explanation: http://www.ibm.com/developerworks/wikis/download/attachments/53871900/Oracle_on_AIX_WebinarFeb2007.pdf?version=2 So, now I'm going to open a ticket with IBM. More as I have it . . . Privileged/Confidential Information may be contained in this message or attachments hereto. Please advise immediately if you or your employer do not consent to Internet email for messages of this kind. Opinions, conclusions and other information in this message that do not relate to the official business of this company shall be understood as neither given nor endorsed by it. -- //www.freelists.org/webpage/oracle-l