FILE SYSTEM BUFFER IN JFS : ON OR OFF : CONCLUSION

From: Raj Sakthi <rajan_sakthi_at_yahoo.com>
Date: Mon, 07 May 2001 10:00:04 -0700
Message-ID: <F001.002FAEC1.20010507094027@fatcity.com>

I know I am slightly late but I have been losing some sleep and lot of
patience with my project(s) so bear with me : ).

The question was
" The ideal mounting option for ORACLE on JFS ? suggested is
RBS & TEMP files : mincache=dsync, convosync=dsync DATAFILES & REDO files :
mincache=direct,convosync=direct "

Before jumping to answers definition of some terms used .

CONVOSYNC : This option determines how synchronous writes are treated

            direct : Bypassing system buffer 
            dsync  : A write operation returns to the
caller after the data has been 
            transferred to external media, but the
inode is not updated 
            synchronously if only the times in the

inode need to be updated
MINCACHE : The mincache mount option determines how ordinary writes are treated.

Can have the same values .

I did some digging around and found some details First :
The answer by Steve ,

Unless your 'db_block_size' is 8192 then you should use direct I/O for
all Oracle file systems regardless of usage. Also because Oracle explicitly
requests synchronous I/O whenever it opens its datafiles, it is the convosync
mount option that counts, rather than the mincache one. Indeed, if you use
'convosync=direct, mincache=dsync' you'll get buffering for trace files
or other stuff that might also reside on your Oracle file systems, which is
probably what you want.

I can't imagine any reason why you would want buffering for rollback
segment datafiles, but assuming your block size is 8K, there is a weak argument
for buffering temporary segment datafiles. Namely that temporary segment
writes are invariably read again, and operating system buffering may save physical
I/O on the reads. Oracle does not normally buffer temporary tablespace I/O and
so with operating system buffering there is no buffering at all. However, if
you machine is dedicated to Oracle and you are willing to allow Oracle to use the
memory directly, then a better approach is to use the memory that might
otherwise be used for operating system buffering of temporary tablespace writes to
increase the 'sort_area_size' and thus avoid those writes entirely.

Christian Bilien :

The advice given looks good to me. Online JFS must indeed be
separately purchased.

In light of the above and my research ,

DATAFILES , RBS , TEMP :
mincache=direct,convosync=direct,nodetainlog REDOLOG , ARCHIVE :
mincache=dsync,convosync=dsync

Any comments welcome .
regards ,
RS

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Author: Raj Sakthi
INET: rajan_sakthi_at_yahoo.com

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