Refresh the documentation to more clear and to account for changes
for made in the recent RHEL/CentOS releases.
- Replaced most ZFS on Linux references with OpenZFS.
- Condensed the list of repositories and made it clear which repos
are updated with new packages and which had been archived.
- Added separate instructions for RHEL/CentOS 6,7 and for RHEL/CentOS
8 and newer since the package manager was changes from yum to dnf.
- Recommend using `yum-config-manager` or `dnf config-manager` rather
than manually modifing the zfs.repo file.
- Converted the important notices to "notes" and reworded them. The
exact commands in the documention were also for much older versions
of ZFS and were removed entirely. This should be less of an issue
with more modern releases.
- Add a comment explaining the modules are automatically loaded
when a pool is detected, but they can always be loaded at boot
time by creating a /etc/modules-load.d/zfs.conf file.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
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