Re: [Virtio-fs] Kudos: productivity boost using virtio-fs

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Harry G. Coin (hgcoin@gmail.com) wrote:
> 
> On 10/1/20 8:51 AM, Dr. David Alan Gilbert wrote:
> > * Harry G. Coin (hgcoin@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? 
> >> 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@redhat.com / Manchester, UK