access to hard drives is "blocked" by writes to a flash drive

[Konstantin Belousov]

On Mon, Mar 04, 2013 at 01:44:30PM +0000, Poul-Henning Kamp wrote:
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> In message <201303040712.r247CejP008718 at gw.catspoiler.org>, Don Lewis writes:
> 
> >Prior to 231160, the syncer thread would call sync_vnode() for the
> >syncer vnode of each mountpoint every 30 seconds [...]
> 
> I agree that the lemming syncer is better, but the fundamental mistake of
> only having one syncer thread is probably the root-cause in this case:
> One camera-grade flash syncing may take (a lot) more than 30 seconds.
> 
> One mountpoint having trouble (of whatever kind) should not affect
> the rest of the mountpoints.
> 
> I'm not sure if the syncer is untangled enough that we can have
> per mount-point threads yet, but as soon as we can, we should do that.

The problem with "wdrain" is not due to any algorithm in the syncer.
I explained it in some details in other mail.
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