I want to experiment with mbcache kernel module, but I'm having trouble finding the documentation for it.

If I understood correctly, mbcache allows the use of a fast SSD disk to act as a transparent cache for much slower hard disks.

Where can I find the documentation?

I'm on Linux 3.0.0-17-generic #30-Ubuntu SMP x86_64


Go for bcache now, not mbcache (kernels 3.10.x, 3.11.0)


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  • Interesting. I wonder if bcache has good resilience after a power outage. One of the problems I face with flashcache is that it takes a fairly long time to flush the cache to my RAID set. A large cache may take longer than my UPS is able to sustain power to the system. However slight chance of this happening, it does influence the size of the cache that I can use. – jippie Aug 29 '13 at 6:05

There doesn't seem to be any documentation other than the source code itself. I wrote to Andreas Gruenbacher and referenced this question but have not received a reply.

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  • I took a peek at the source code, but the comment isn't really helpful. The userland tools are not mentioned at all (but that is no surprise). Hopefully the mbcache project will share documentation shortly. – jippie Apr 19 '12 at 7:52

mbcache doesn't allow you to cache one block device using another, rather it is an in-memory cache, which is used to speed up filesystem performance, and it used directly and automatically by filesystems without any user configuration. At the time of writing, it's only used by the ext4 filesystem.

The main kernel modules which do what you are intending (e.g. cache slow block devices using fast ones) are bcache and dm-cache (which is usually managed using the lvmcache user space tools).

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