Re: SCSI vs. IDE performance test

Martijn van Oosterhout <kleptog@svana.org> writes:

> On Tue, Oct 28, 2003 at 12:17:59AM -0500, Tom Lane wrote:
> > "Rick Gigger" <rick@alpinenetworking.com> writes:
> > > Do serial ATA drives suffer from the same issue?
> >
> > Um, not an expert, but I think ATA is the same as IDE except for bus
> > width and transfer rate.  If either one allows for multiple concurrent
> > read/write transactions I'll be very surprised.
>
> Well, some googleing around seems to indicate that Serial ATA I/ATA-6 has
> Tagged Command Queueing (TCQ) which is adding this feature specifically.
> Whether it is a mandatory part of the spec I don't know.

The post on linux-kernel from the maxtor guy seemed to indicate we would have
to wait for ATA-7 drives (which are not out in the market yet) before the
features we really need are there.

Currently the linux-kernel folks are talking about how to integrate an IDE
SYNC operation into the world. It looks like filesystems with journals will
issue an IDE SYNC to checkpoint the journal, but it doesn't really look like
they're planning to hook it into fsync unless people speak up and explain what
databases need in that regard. However SYNC flushes the entire cache and means
that all other writes are blocked until the SYNC completes.

Apparently the feature needed to *really* implement fsync is called FUA which
would give real feedback of the status of the write without preventing all
other writes from proceeding. That's what isn't going to appear until ATA-7.

All this is from a few posts on linux-kernel. e.g.:

http://www.ussg.iu.edu/hypermail/linux/kernel/0304.1/0450.html

--
greg