I think a natural follow-up question is "Why Red Hat does not have engineers to support btrfs?" That is, if the lack of engineers is a symptom, what is the cause?

I'm pretty sure, had RH wanted they could either hire or assign engineers to maintain the btrfs code, take care of patches from upstream, etc. So why didn't that happen? I wonder what is your opinion on that.

I see a bunch of possibilities (not necessarily independent ones):

1) Politics. Perhaps RH wants to kill btrfs for some reason?

I see this as rather unlikely, as RH does not have a competing solution (unlike in the Jigsaw controversy, where they have incentives to kill it in favor of the JBoss module system).

2) Inability to hire enough engineers familiar with btrfs, or assign existing engineers.

Perhaps the number of engineers would be too high, increasing costs. Especially if not only to maintain the RHEL kernels, but to contribute to btrfs and move it forward.

Or maybe there's a pushback from the current filesystems team, where most people are xfs developers?

3) Incompatible development models.

If each release requires a rebase, perhaps supporting btrfs would require too much work / too many engineers, increasing costs? I wonder what Suse and others are doing differently, except for having in-house btrfs developers.

4) Lack of trust btrfs will get mature enough for RHEL soon.

It may work for certain deployments, but for RHEL customers that may not be sufficient. That probably requires a filesystem performing well for a wider range of workloads.

5) Lack of interest from paying RHEL customers.

Many of our customers have RHEL systems (or CentOS / Scientific Linux), and I don't remember a single one of them using btrfs or planning to do so. We only deal with database servers, which is a very narrow segment of the market, and fairly conservative one when it comes to filesystems.

But overall, if customers are not interested in a feature, it's merely a pragmatic business decision not to spend money on it.

6) Better alternatives available.

I'm not aware of one, although "ZFS on Linux" is getting much better.

So I tend to see this as a pragmatic business decision, based on customer interest in btrfs on RHEL vs. costs of supporting it.