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Re: WAPBL and "cache flush not supported by backend"

Thanks for the clarification.  I will see if I can find out any
details from my VPS provider about their dom0 setup so I can assess
the risk, but I suppose I'll probably turn it off to be safe.  I'm not
untarring pkgsrc every day so the performance hit won't make to big of
a difference.

So, what is the ultimate cause of cache flushing not being supported?
Is this something to do with the configuration of dom0, which could in
principle be changed?  Or is NetBSD missing some driver support and
there's nothing that can be done without it?


On Mon, 18 Feb 2013
10:02:28 +0100 Manuel Bouyer <> wrote:

> The warning is there for a reason. In theory, this issue could lead
> to filesystem corruption when a poweroff occurs with data in
> the disk or dom0 cache (if dom0 is doing write back) that are not yet on
> platters (WAPBL use cache flush as a barrier, to make sure all data before
> the upcoming writes are on disk and things cannot be reordered).
> Whenever this is a real problem depends on dom0 setup/behavior, and hardware
> (the dom0 could turn off the write back disk cache, or the storage
> could be a RAID controller with battery-backed cache).

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