[cdwg] Lustre Maintenance Release Plan

[Christopher J. Morrone]

Lustre Maintenance Release Plan
-------------------------------

Lustre maintenance branches host the releases of lustre that we shall
advertise to the general public as "stable" releases.  The goal of a
maintenance branch is to include only bug fixes, to ensure a stable
releases for a significant period of time.

We currently have a development cadence that puts out a "feature"
release of Lustre every 6 months.  This is going reasonably well, and we 
plan to continue that process.  However, we do not have the resources to 
ensure that every six month release is entirely bug-free, nor do we have 
the resources to add a new branch every six months that will receive 
only bug, and be maintained for years.  We are not able to reasonably 
support and test that many branches in parallel at our current level of 
investment, nor would we wish to, as the testing requirements rise 
exponentially as the number of supported branches increases.

We have decided that every third feature release, occurring every 18
months, will also be the beginning of a maintenance branch.  Tagged
maintenance releases along the maintenance branch will occur on an
as-needed basis, according to the demands of discovered bugs and their
severity.  It is likely that tags will occur more frequently early in
the branch's lifetime, and taper off in the later months and years.

We plan to make the initially advertised lifetime of a maintenance
branch three years.

We agreed that Lustre 2.4 will begin the next maintenance branch, which
has a targeted release date of the end of March, 2013.

None of this precludes ad-hoc maintenance releases on other branches. 
For instance, there was discussion in the CDWG that some institutions 
plan to run Lustre 2.3, and may need a "mini-maintenance" release to 
hold them over until Lustre 2.4.  We just note that those 
"mini-maintenance" releases will be made as the participants have the 
time and desire to work on them, and that they will be made on an 
as-needed, and ad-hoc manner.

We will continue to refine our terminology to help avoid confusion.

To reiterate, out basic plan of record is:

  - Next official maintenance branch will be 2.4 (end of March 2013)
  - Official maintenance branches will start every 18 months
  - Official maintenance branches will be supported for 3 years

Chris