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parameter to disable direct io

marakr asked
I am working with OPS (v. in Tru64 v 5.1.
I would like to know which parameters of the init.ora are related to direct io access?  Which parameters should I set in order to disable direct io?
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For disable direct io , you have to use the paramter async_write=<no>
Asynchronous I/O allows one oracle  Server database writer to write to multiple disks simultaneously, thus increasing disk throughput. The DBWR process sends  
multiple writes to multiple drives without waiting for the previous writes to
finish. It can use all disks simultaneously. With 10 disks, for example, 10
asynchronous writes can take place in the same amount of time as a single  
synchronous write.  

Note: Oracle recommends you set the parameter DB_WRITERS = 1 if you have set
the parameter ASYNC_WRITE=1.

You will get more info about this in your platform specfic docs.

Hope this helps


You mention asynch io, and I am interest on direct io.  What is the relationship between them? I am a bit confuse.  
In my point of view, direct IO is when you want to write to disk without using the UBC from operational system (UBC = unified buffer cache, it is the control of the shared memory by the operational system - by the way, I am dealing with Compaq Tru64).  Asynchronous IO I believe is exactly what you have explained.  I thought they were different things...
So, how do both definitions relate to each other?
Else, is it still async_write that disables the direct IO?
Since you are usinf tru64  you have to defined
 _TRU64_DIRECTIO_DISABLED = TRUE in the init file.

Also you may also apply patch on oracle

Oracle with patch 1523186

This is the doc which i grab from oracle support.

Doc ID:  Note:62343.1
Subject:  Compaq Tru64 UNIX 5.0/5.1 Update
Type:  FAQ
 Content Type:  TEXT/PLAIN
Creation Date:  20-AUG-1998
Last Revision Date:  19-JUL-2001

Tru64 UNIX 5.0 / 5.1 Update

Tru64 UNIX 5.0/5.0a/5.1 are available and ship under the new name of
Compaq Tru64 UNIX (as 4.0f did).

  -- OPS: Oracle with OPS is not supported or certified on Tru64 UNIX 5.0
     because TCR 5.0 (Compaq's cluster software) is in "limited distribution" only, and
     OPS is dependent on the TCR component.

  -- Non-OPS: 8.1.7, 8.1.6, 8.1.5, 8.0.6, 8.0.5 and 7.3.4 are certified on 5.0.

  -- OPS: OPS is certified on Tru64 UNIX versions 5.0a and above.
     You must install Compaq's Patchkit 1 or Compaq patch #804369
     on top of 5.0a however to support OPS. Both patches are only available
     from Compaq.

     Oracle versions supported for OPS on 5.0a are 7.3.4, 8.0.5, 8.0.6, 8.1.5
     8.1.6 and 8.1.7. All Oracle patchsets for these versions are also certified
     with the exception of and in OPS mode. If you are running
     OPS on 5.0a with 8.1.6, these patchsets are fully supported, although the
     full set of certification tests has not been run.

  -- Non-OPS: 8.1.7 8.1.6, 8.1.5, 8.0.6, 8.0.5 and 7.3.4 are certified on 5.0a.

  -- OPS: 8.1.7. 8.1.6, 8.1.5, 8.0.6 and 7.3.4 are certified with 5.1.  
  -- Non-OPS: 8.1.6, 8.1.5, 8.0.6 and 7.3.4 are certified on 5.1.

 + and patchsets are not certified with OPS on any version of
   Tru64 UNIX.
Support for directIO Advfs in 5.0a/5.1
With 5.0a/5.1, Advfs filesystems allow directIO allowing similar
performance gains to that obtained with raw devices. However to
use this feature in Oracle, an Oracle patch will be required.
The fix has been documented for inclusion in 8.1.7 in bug 1394690. Fixes
to older verions of Oracle are also available. See [NOTE:132391.1] for more

It is important that a Compaq patch is also installed before using directIO.
See [NOTE:132391.1] for more details.

Support for Advfs shared filesystems in 5.0a/5.1
With 5.1/5.0a, Advfs filesystems (also known as Cluster File Systems or CFS)
can be shared between nodes on a TruCluster. Consequently you can now use
filesystems for Oracle datafiles, controlfiles and redologs in an OPS
environment. You no longer need to use raw devices.

However with 5.0a, Oracle does recommend or support using shared filesystems
for OPS.  CFS is recommended for OPS with 5.1 however.

The reason why 5.0a is not recommended is due to the different IO models
used for implementing CFS on 5.0a/5.1:

At 5.0a a file system is owned (served) by a single node. Compaq call this
the "Served IO Model".  The owning node is the only node that can perform
IO to that file system, on an OPS system this could flood the interconnect
with disc IO.

In 5.1 the "Concurrent Direct IO Model" is used, this allows all nodes to
perform their own IO to existing blocks. The first IO to a new block
(ie a create/extend datafile) is still served by the owning node.

Further details regarding Tru64 UNIX
Details about Tru64 UNIX can be found from the Compaq web site:


Specific details about Tru64 UNIX 5.0 can be found at:



Thank you very much.  I couldn't ask for a better answer.
Thanks again.

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