From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Thu, 1 Oct 2020 17:26:18 +0100 From: "Dr. David Alan Gilbert" Message-ID: <20201001162618.GN2807@work-vm> References: <20200929185015.GG220516@redhat.com> <20201001135129.GG2807@work-vm> <3deb375c-e234-f83c-159f-cebdd3a1876e@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Disposition: inline Content-Transfer-Encoding: quoted-printable In-Reply-To: <3deb375c-e234-f83c-159f-cebdd3a1876e@gmail.com> Subject: Re: [Virtio-fs] Kudos: productivity boost using virtio-fs List-Id: Development discussions about virtio-fs List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Harry G. Coin" Cc: virtio-fs@redhat.com * Harry G. Coin (hgcoin@gmail.com) wrote: >=20 > 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.=C2=A0= =C2=A0 Why?=C2=A0 > >> Because the underlying file system is never corrupted (though individu= al > >> file contents may be, the file system itself is protected).=C2=A0=C2= =A0 For > >> example, using btrfs' snapshot ability in the underlying file system a= nd > >> 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 >=20 > The 3 host chassis I've set up so far to work with this has a=A0 btrfs > file system in a raid-1 setup.=A0 Btrfs does a good job with xattr support > which virtio-fs can be set to use well. >=20 > I have several vm's running on each chassis, each using virtio-fs.=A0 On > the host, there is a sub-volume for each vm.=A0 The vms=A0 use kernel > booting, and huge pages.=A0 So, on the bare-metal host, a simple 'btrfs su > snapshot generates an 'almost free' (from a > resource perspective) look at the entire vm.=A0 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.=A0 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.=A0 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.=A0=A0 Delete the 'frozen' state > snapshot, make a new=A0 snapshot of the known good snapshot, reboot the vm > and the dev cycle can continue.=A0 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. >=20 > 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.=A0 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 >=20 >=20 >=20 >=20 > >> 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 > >> Virtio-fs@redhat.com > >> https://www.redhat.com/mailman/listinfo/virtio-fs >=20 --=20 Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK