Re: Maximum transaction rate

On Fri, 2009-03-13 at 11:41 -0700, Ben Chobot wrote:
> On Fri, 13 Mar 2009, Joshua D. Drake wrote:
>
> >> It seems to me that all you get with a BBU-enabled card is the ability to
> >> get burts of writes out of the OS faster. So you still have the problem,
> >> it's just less like to be encountered.
> >
> > A BBU controller is about more than that. It is also supposed to be
> > about data integrity. The ability to have unexpected outages and have
> > the drives stay consistent because the controller remembers the state
> > (if that is a reasonable way to put it).
>
> Of course. But if you can't reliably flush the OS buffers (because, say,
> you're using LVM so fsync() doesn't work), then you can't say what
> actually has made it to the safety of the raid card.

Wait, actually a good BBU RAID controller will disable the cache on the
drives. So everything that is cached is already on the controller vs.
the drives itself.

Or am I missing something?

Joshua D. Drake

>
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