[OpenAFS] releasing ro volumes with small deltas

Russ Allbery rra@stanford.edu
Mon, 30 Aug 2010 12:54:43 -0700

olin.afs.7ia@shivers.mail0.org writes:

> Now I have VS bytes stored on server 1, and another VS bytes on server 2.

> I then change *one* *tiny* file on read/write volume VRW. What I mean
> is:  every file on VRW is identical to its original state, except for a
> single small file (say, a 1KB file). Now I re-release the readonly
> volume VRO, to both partitions, on servers 1 & 2.

> My question is: how much data gets shipped over the net to update volume
> VRO on server 2? Does server 1 ship the entire volume (VS bytes), or
> does it ship just the changed file (about 1K bytes)?

It ships the same amount that would be shipped by an incremental backup,
which I think may be slightly worse than only shipping the changed file
but is much closer to that than sending the whole volume.

> I am interested in this, because I'm considering setting up a readonly
> volume for my music collection. It'd be nice to have the whole thing
> replicated at home -- then I would be insulated from network outages. If
> I buy a new CD and rip it into my music volume, I then have to
> re-release the readonly volume after adding the new album's worth of
> music. I don't want the *whole collection* (about 900GB) of bits to get
> jammed through my pitiful cable modem when I do this. I'd like half a
> gigabyte of bits (the new music, that is) to get shipped over the net
> from the main server to my home-net's replica server.

vos release should basically do what you want here, as long as you don't
use the -f option (which forces a full update).

Russ Allbery (rra@stanford.edu)             <http://www.eyrie.org/~eagle/>