Re: shutdown sequence and UPS poweroff

[David Brownlee <abs%absd.org@localhost>]

On Mon, 9 Jan 2023 at 20:30, David Holland <dholland-tech%netbsd.org@localhost> wrote:
>
> On Fri, Jan 06, 2023 at 10:13:36AM -0500, Greg Troxel wrote:
>  > Does it seem reasonably safe that mountall through root will be fast, < 10s?
>
> We've been seeing scattered reports of unmounting taking fast amounts
> of time, particularly on nvme devices, and I don't think we know why
> yet.
>
> It's a bug, but since not cutting the power to SSDs midflight is one
> of the primary reasons to have a UPS these days... seems like a
> dangerous on in this context. So it seems like a good idea to be
> cautions.
>
> Not sure what to recommend. The last time there was an issue like this
> (which turned out to be a bad bug with cached data not being written
> back until unmount time) it was possible to trigger the writing by
> attempting an unmount you know will fail with EBUSY, but I don't think
> we've ascertained if that works this go.

If only we had a reliable way to remount filesystems from read-write
to readonly after flushing data, that could be an option on shutdown,
then the ups command could be triggered with no writable filesystems
:-P

David