Server related

How do I completely reset a cluster ?

The simplest way is to create a new metadata file. Go to your metadata directory on your current master server (look at the DATA_PATH in the mfsmaster.cfg file), than stop the master and create a new empty metadata file by executing:

echo -n "MFSM NEW" > metadata.mfs

Start the master and your cluster will be clear, all remaining chunks will be deleted.

How do I create a full backup of all my metadata (in case of recreating a master etc...)

Copy your data directory somewhere safe (default path: /var/lib/mfs).

Files you should be interested in keeping are primarily:

• metadata.mfs - your metadata set in binary form. This file is updated hourly + on master server shutdown. You can also trigger a metadata dump with lizardfs-admin save-metadata HOST PORT, but an admin password needs to be set in the mfsmater.cfg first.
• sessions.mfs - additional information on user sessions.
• changelog*.mfs - changes to metadata that weren’t dumped to metadata.mfs yet.

How do I speed up/slow down the main chunk loop execution during which chunks are checked if they need replication/deletion/rebalance/etc

Adjust the following settings in the master server configuration file:

CHUNKS_LOOP_PERIOD
    Time in milliseconds between chunks loop execution (default is 1000).

CHUNKS_LOOP_MAX_CPU
    Hard limit on CPU usage by chunks loop (percentage value, default is 60).