doc/rados: erasure-code-lrc corrections
- Clarified / corrected jerasure recovery characterization cf. https://library.eecs.utk.edu/storage/125phpw0xFqAut-cs-07-603.pdf
- Capitalization
- Word choice: OSDs are discrete / cardinal, so "fewer" instead of "less"
- Reworked a few phrases to be less stilted
Signed-off-by: Anthony D'Atri <anthony.datri@gmail.com>
Since kraken, Ceph enforces a 1:1 correspondence between CRUSH ruleset and
CRUSH rule, so effectively ruleset and rule are the same thing, although
the term "ruleset" still survives - notably in the CRUSH rule itself, where it
effectively denotes the number of the rule.
This commit updates the documentation to more faithfully reflect the current
state of the code.
Fixes: http://tracker.ceph.com/issues/20559
Signed-off-by: Nathan Cutler <ncutler@suse.com>
1) ruleset is an obsolete term, and
2) crush-{rule,failure-domain,...} is more descriptive.
Note that we are changing the names of the erasure code profile keys
from ruleset-* to crush-*. We will update this on upgrade when the
luminous flag is set, but that means that during mon upgrade you cannot
create EC pools that use these fields.
When the upgrade completes (users sets require_osd_release = luminous)
existing ec profiles are updated automatically.
Signed-off-by: Sage Weil <sage@redhat.com>
LRC now uses Jerasure as the default EC backend. But it is actually
possible to switch to other backend like Isa using the low level
configuration. This commits Adds documents on how to specify the EC
backend in each LRC layer:
Signed-off-by: Yuan Zhou <yuan.zhou@intel.com>
