This feature is poorly supported, and causes grief for cache development due to
how it #ifdef’s with the system. There are plans for a new system that would
make the concept of cache hierarchies generic. In the mean time, the suggestion
is that if you need this, you use one of
1) Assigning content to volumes and disks via our existing configs.
2) Use Linux’s bcache feature, which comes with Linux 3.10 or later. I
suspect e.g. ZFS has something similar.
3) Use a third party system to implement the hybrid device (e.g. flash
cache or EnhanceIO.
This is tracked in the Jira:
https://issues.apache.org/jira/browse/TS-3541
as well as
https://issues.apache.org/jira/browse/TS-3165
Unless we hear otherwise within 1 week, this will be implemented for 6.0.0. We
will update the Wiki with the library version dependencies (see below).
— Leif
