Re: [Nbd] Question about the expected behaviour of nbd-server for async ops

[Alex Bligh <alex@...872...>]

--On 29 May 2011 19:54:35 +0200 Wouter Verhelst <w@...112...> wrote:

> > Which just means that a CoW based filing system or sparse files don't
> > support FUA. The idea of a FUA is that it is cheaper than a FLUSH. But
> > if nbd-server does fsync() in both cases then it is pointless to
> > announce FUA support.
>
> No, that's not entirely true. With a FLUSH, you need to ensure that
> whatever the FLUSH would cover is flushed to disk; with a FUA, you need
> to ensure the same thing for just one call, which is easier to do.

Indeed. And even if we were limited to fsync() by something other than
my laziness, then we'd still only need to fsync() one file, rather than
every file (in a device spanning multiple files).

--
Alex Bligh