[Virtio-fs] Kudos: productivity boost using virtio-fs
Dr. David Alan Gilbert
dgilbert at redhat.com
Thu Oct 1 16:26:18 UTC 2020
* Harry G. Coin (hgcoin at gmail.com) wrote:
>
> On 10/1/20 8:51 AM, Dr. David Alan Gilbert wrote:
> > * Harry G. Coin (hgcoin at gmail.com) wrote:
> >> Though it's likely been written before:
> >>
> >> Virtio-fs is a wonderful productivity boost in development environments
> >> in which unrelated deadlocks, crashes and hard-lockups happen.  Why?Â
> >> Because the underlying file system is never corrupted (though individual
> >> file contents may be, the file system itself is protected).  For
> >> example, using btrfs' snapshot ability in the underlying file system and
> >> comparing 'before and after' crashes creates a powerful debugging tool.
> > Thanks!
> >
> > I'm curious, can you describe a bit more about how you're using it with
> > btrfs - I don't think we've had anyone describe that before.
> > (We mostly use it with overlayfs via the various container tools).
> >
> > Dave
>
> The 3 host chassis I've set up so far to work with this has a btrfs
> file system in a raid-1 setup. Btrfs does a good job with xattr support
> which virtio-fs can be set to use well.
>
> I have several vm's running on each chassis, each using virtio-fs. On
> the host, there is a sub-volume for each vm. The vms use kernel
> booting, and huge pages. So, on the bare-metal host, a simple 'btrfs su
> snapshot <vm sub volume> <snap name> generates an 'almost free' (from a
> resource perspective) look at the entire vm. Various risky experimental
> things go on in the vm, which could lead to file system corruption owing
> to deadlocks and hard freezes and race conditions. However with
> virtio-fs, when that happens, all I need to do on the host is make a
> another snapshot of the 'frozen' vm, stop the vm. Then I can compare
> the exact state of the files at the time of the freeze with the 'known
> good' versions at the snapshot time. Delete the 'frozen' state
> snapshot, make a new snapshot of the known good snapshot, reboot the vm
> and the dev cycle can continue.
OK, nice.
> Even if the cause of the freeze wasn't evident in the file system
> deltas, knowing there isn't corruption in the underlying fs is a big
> time saver.
>
> I expect when dax makes it out of the development bubble this
> configuration will be a very high performance, easy to maintain, high
> security arrangement. Much harder to 'break out' of a vm than the
> various container options.
Yeh; dealing with stuff that corrupts your install isn't fun;
thanks for the explanation!
Dave
>
>
>
>
> >> I suspect most folks involved in virtio-fs know this, but it's worth
> >> putting in the record for new folks.
> >>
> >> Harry
> >>
> >>
> >>
> >>
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>
--
Dr. David Alan Gilbert / dgilbert at redhat.com / Manchester, UK
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