CentOS 7 + bcache

Fizzadar asked:

bcache was rolled into the 3.10 mainline kernel. I’ve just installed CentOS 7 with 3.10.0-123.4.4.el7.x86_64. However, after creating the cache devices I realised they were’t attached. Turns out /sys/fs/bcache doesn’t exist – ie it’s not enabled in the kernel, but why? I believe it’s enabled by default in Ubuntu/etc…

My answer:

Red Hat Enterprise Linux 7 was forked from Fedora 19, and in that release bcache support was minimal, experimental and buggy. It currently isn’t planned to be complete until Fedora 22. As a general rule, Red Hat does not ship features in RHEL which aren’t production-ready, even as a technology preview.

If I were to guess, I would expect to see this appear in RHEL as a technology preview sometime around 7.2, or 7.3, or perhaps even 7.4, depending on how development progresses — and importantly, depending on whether Red Hat customers ask for it… or more likely I’m totally wrong.

Red Hat’s current stance on bcache is:

bcache is another option available in the Fedora 22 Linux distribution and merged into the upstream Linux kernel. It is not currently viewed by Red Hat as Enterprise ready as a supported technology.

Red Hat instead supports dm-cache and lvmcache as of RHEL 6.7 and 7.1.

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