Re: scsi vs ide performance on fsync's

Stephen C. Tweedie
2001-03-07T21:01:17Z

Hi,

On Wed, Mar 07, 2001 at 09:15:36PM +0100, Jens Axboe wrote:
> On Wed, Mar 07 2001, Stephen C. Tweedie wrote:
> >
> > For most fs'es, that's not an issue. The fs won't start writeback on
> > the primary disk at all until the journal commit has been acknowledged
> > as firm on disk.
>
> But do you then force wait on that journal commit?

It doesn't matter too much --- it's only the writeback which is doing
this (ext3 uses a separate journal thread for it), so any sleep is
only there to wait for the moment when writeback can safely begin:
users of the filesystem won't see any stalls.

> A barrier operation is sufficient then. So you're saying don't
> over design, a simple barrier is all you need?

Pretty much so. The simple barrier is the only thing which can be
effectively optimised at the hardware level with SCSI anyway.

Cheers,
Stephen