Ext3 users - Mar 2007 - EXT2 vs. EXT3: mount w/sync or fdatasync

My application always needs to sync file data after writing. I don't want
anything handing around in the kernel buffers. I am wondering what is the best
method to accomplish this.
 
 1. Do I use EXT2 and use fdatasync() or fsync()?
 
 2. Do I use EXT2 and mount with the "sync" option?
 
 3. Do I use EXT2 and use the O_DIRECT flag on open()?
 
 4. Do I use EXT3 in full journaled mode, where the data and metadata are
journaled? In this case, is the journaled data sync'd or async'd? When
the journal commits the data to the file system, is that sync'd or dumped
into kernel buffers?
 
 5. Since I will always be syncing the data, does it make any sense to use EXT3?
It feels like the EXT3 journal would be unnecessary.
 
 Thanks in advance
 
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On Mar 21, 2007  16:51 -0700, brian stone wrote:
> My application always needs to sync file data after writing. I don't
want anything handing around in the kernel buffers. I am wondering what is the
best method to accomplish this.
>  4. Do I use EXT3 in full journaled mode, where the data and metadata are
journaled? In this case, is the journaled data sync'd or async'd? When
the journal commits the data to the file system, is that sync'd or dumped
into kernel buffers?
>  
>  5. Since I will always be syncing the data, does it make any sense to use
EXT3? It feels like the EXT3 journal would be unnecessary.
In theory, ext3 + data=journal will give you the best performance, because
sync IO will always be linear IO to the journal.  Unless your filesystem is
constantly busy, then the writes to the filesystem can happen asynchronously
after being committed to the journal without danger of being lost.

That said, nothing better than benchmarking your app with different
filesystem options to see which one is best.

Cheers, Andreas
--
Andreas Dilger
Principal Software Engineer
Cluster File Systems, Inc.