Why Oracle 11g need forcedirectio option?

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Special Forums UNIX and Linux Applications Why Oracle 11g need forcedirectio option?
# 1  
Old 09-16-2011
Why Oracle 11g need forcedirectio option?

I've spent one day to find solution for a nfs mounting problem with Oracle11g installation. Finally, I've found that the missing options was

My question is, why this options is mandatory when we talk about datafiles installation?

# 2  
Old 09-16-2011
One of the reasons is outlined in the following MOS note (and it's not only on HP, as the note title may seem to imply),
I don't know if it applies to your case:

Potential Lost Writes: RAC on NAS using NFS may not use DIRECTIO or HP on NFS (Doc ID 566545.1)

Last edited by radoulov; 09-16-2011 at 10:54 AM..
# 3  
Old 09-21-2011
A bit of late reply, but I tried to stay away, as much as I could, from NFS overall, when we talk about large scales, RAC in our case.

From the manpage of mount_nfs:

If the filesystem is mounted using forcedirectio, data is transferred directly between client and server, with no buffering on the client. If the filesystem is mounted using noforcedirectio, data is buffered on the client. forcedirectio is a performance option that is of benefit only in large sequential data transfers. The default behavior is noforcedirectio.
# 4  
Old 09-26-2011
Thanks guys,
but both did not answer my question Smilie
I asked whe it is mandatory.
As sysgate said, mount command indicates it as a performance options, so I asked myself... is it a really mandatory option?
# 5  
Old 09-26-2011
The Oracle 11g documentation Checking NFS Mount and Buffer Size Parameters for Oracle Clusterware points to My Oracle Support bulletin 359515.1 which states:


The purpose of this bulletin is to document the options with which the NAS systems should be mounted. 
This note does not cover the new dNFS feature that was introduced in 11g

They use the verb "should" (not "must"). From Request for Comments: 2119:

3. SHOULD   This word, or the adjective "RECOMMENDED", mean that there
   may exist valid reasons in particular circumstances to ignore a
   particular item, but the full implications must be understood and
   carefully weighed before choosing a different course.

That said, it's worth noting that all this applies to GI and RAC (it's not specified if it applies to a regular databases as well).

Hope this helps.
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