Re: 64 K write access grouped in a single disk access ?

["Stephen C. Tweedie" <sct redhat com>]

Hi,

On Mon, Jun 03, 2002 at 02:13:05PM +0200, chacron1 wrote:
 
> Hi Stephen,
 
> I would like to know the behavior of ext3 for a write() request  used
> with
> O_SYNC
> for 64 K in term of disk access method:
> - is there a chance to have only one disk access (instead of 16 x 4 K
> corresponding to each mapped page ) or at maximum two in journaled mode
> ?

Journaled mode is guaranteed to produce more writes: it will write to
the journal immediately, _and_ will eventually write to the backing
store.

For overwrites to already-allocated data, ordered data mode ought to
allow for better coalesced writes to the filesystem, as there won't be
a forced journal flush in that case (for O_SYNC, we don't bother
updating the inode in the journal if all we changed was the mtime
timestamp.)

Cheers,
 Stephen