* Harry G. Coin ([email protected]) wrote: > > On 10/1/20 8:51 AM, Dr. David Alan Gilbert wrote: > > * Harry G. Coin ([email protected]) 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 > >> > >> > >> > >> > >> _______________________________________________ > >> Virtio-fs mailing list > >> [email protected] > >> https://www.redhat.com/mailman/listinfo/virtio-fs > -- Dr. David Alan Gilbert / [email protected] / Manchester, UK _______________________________________________ Virtio-fs mailing list [email protected] https://www.redhat.com/mailman/listinfo/virtio-fs
