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Re: usrmerge -- plan B?





On 26/11/2018 14:44, Adam Borowski wrote:
On Mon, Nov 26, 2018 at 09:29:50AM -0500, Michael Stone wrote:
On Mon, Nov 26, 2018 at 03:08:09PM +0100, Marco d'Itri wrote:
I disagree both that simple testing (that you could do with a KVM
snapshot as well) would be hard and I disagree that the benefits of
merged-/usr would be minor.
Nobody has thus far pointed out a single benefit to someone merging usr on
an ordinary system.
Nor for clusters, for that matter.  I don't get how having the /usr part of
the filesystem (no /var, /lib, /etc, etc) would help --

Moving config from /etc to below /usr becomes useful for containers, and hence clusters.

(I suspect this might be the most useful bit of a merged-/usr concept in the long run).

containers become important for clusters - we are now using Singularity in our HPC clusters. Singularity is a development of Docker that allows for non-root container execution; we can build containers on our laptops, etc (requiring root), and copy them to the cluster, where they will run, even connecting with mpiexec / slurm ,etc

This is important because we've never used Debian on our high-end clusters before - they all have parallel filesystems for which we need special kernel modules (for DDN or Panasas, or Lustre), supported by the vendor. So we needed to use the vendors version of SuSE /Redhat/Centos ,etc. And building complex applications was then a pain in  the neck.

Now, we can build a container on a laptop, with Debian inside, and run it on a 1000-node cluster.  Its realistic to see million-core jobs on Debian in the future.

So, while supporting containers may support a minority of users, I suspect some will be big users, and as library and app complexity grows, its an important Debian use-case.

Alastair

--
Alastair McKinstry, <alastair@xxxxxxxx>, <mckinstry@xxxxxxxxxx>, https://diaspora.sceal.ie/u/amckinstry
Commander Vimes didn’t like the phrase “The innocent have nothing to fear,”
 believing the innocent had everything to fear, mostly from the guilty but in the longer term
 even more from those who say things like “The innocent have nothing to fear.”
 - T. Pratchett, Snuff