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Description of problem:
There is missing information in manpage about link between block map cache size and logical thread count. The default 128MB block map cache can support up to 8 logical threads (try-error), so to have more logical threads, user also has to increase block map cache size. I assume this could be done automatically, increasing default block map cache size if it is not large enough. But never the less this information should be in manpage.


Version-Release number of selected component (if applicable):
vdo-6.1.0.34-8

How reproducible:
100%

Steps to Reproduce:
1. vdo create --device DEVICE --name NAME --vdoLogicalThreads 100

Actual results:
vdo: ERROR - Insufficient block map cache for vdo
No hint in manpage about this

Expected results:
vdo: ERROR - Insufficient block map cache for vdo / or VDO succesfully creted with larger block map cache size
Information in manpage about this link

Additional info:

The "vdo" man page does mention this under the --blockMapCacheSize option, but the doc for --vdoLogicalThreads doesn't touch on it. Easy enough to fix...

vdo-6.1.0.55-10

manpage:
--blockMapCacheSize "The cache must be at least 16MB per logical thread. Note that there is a memory overhead of 15%."
--vdoLogicalThreads "A logical thread count over 8 will require explicitly specifying a sufficiently large block map cache size, as well."

--help:
--vdoLogicalThreads "A logical thread count over 8 will require explicitly specifying a sufficiently large block map cache size, as well."

The info about logical threads is missing at --helps --blockMapCacheSize, but it is in manpage, which is enough with this specific info. There is enough info at --vdoLogicalThreads in both manpage and --help.

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHEA-2018:0871