metadata.mfs - Information about the filesystem objects (files, directories, links, etc.) is kept in a special metadata file, called metadata.mfs. When the master server starts up it first reads this entire file into RAM. When the master server exits cleanly it writes out the entire metadata from the RAM back to this file and renames it to metadata.mfs.
metadata.mfs.back - When master server is started , it will read a file metadata.mfs and initiate metadata.mfs.back file from its last state. During normal operation on a master server, all pending changelogs are written to this file on an hourly basis at the top of the hour. It is highly recommended to make an hourly copy, preferably at [HH]:30 and keep last 24 copies of this file and possible backup away from Master srever. In a very rare circumstances, if master server or metalogger servers are beyond recovery for any reason, these hourly backed up files can be used to recover MFS Filesystem to its last known good state.
changelogs.mfs* - These are changelog files written to the disk time to time. These change logs are merged and written to metadata.mfs.back file on an hourly basis. Backup metaloggers sync these files and keep themselves up to date on a regular basis.
These changelog files are used to recover the metadata.mfs.back file in the event the master server process is killed or exits uncleanly, such as when the system crashes or due to a power failure. The changes following the last full metadata save from RAM to the metadata.mfs.back file are replayed into the main metadata.mfs file using the mfsmetarestore utility. The mfsmaster observes a crashed state with the absence of the metadata.mfs file and the presense of the metadata.mfs.back file, and informs you a recover operation is required.
mfsdata.mfs.emergency - It may happen that in the metadata directory you'll find a file mfsdata.mfs.emergency. The file is created only when it was impossible to save the mfsdata.mfs.back file, probably due to some write error. In such a situation you should first make sure there is available space on the disk and make backups of all the metadata files. Later delete mfsdata.mfs.back, change mfsdata.mfs.emergency tomfsdata.mfs.back and run mfsmetarestore -a.
For recovery from crashed master do next command:
mfsmetarestore -a -d /var/mfs #-- /var/mfs is a location where master meta data are written
If you've find mfsdata.mfs.emergency file in metadata folder do next:
delete mfsdata.mfs.back, change mfsdata.mfs.emergency tomfsdata.mfs.back and run mfsmetarestore -a.