Subject: Re: twe status queries?
To: der Mouse <mouse@Rodents.Montreal.QC.CA>
From: Daniel Carosone <>
List: tech-kern
Date: 12/03/2005 07:26:52
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On Fri, Dec 02, 2005 at 01:37:25PM -0500, der Mouse wrote:
> However, I'm seeing a tremendous performance difference between ld0 and
> ld1.

Yup. Sadly, twe(4)'s only do their "R5 fusion" trick for one ld.

This is the trick that lets them avoid r/m/w cycles without using lots
of nvram cache on the card: write requests that would trigger this are
queued, but deferred and not processed until other writes are
collected to make up a full stripe, or a timeout occurs.

It's the same thing an nvram cache would do, but uses the host's
memory by not pretending the writes have completed.

As you can see, r/m/w's are expensive, and it makes quite a difference
- especially if your fs isn't aligned with the raid stripe size for
data as well as small metadata writes.

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