lizardfs(7)

NAME

lizardfs - a networking, distributed, highly available file system

DESCRIPTION

LizardFS is a networking, highly available, distributed file system. It spreads data over several physical localisations (servers), which are visible to a user as one resource. For standard file operations LizardFS acts as other Unix-alike file systems. It has hierarchical structure (directory tree), stores files’ attributes (permissions, last access and modification times) as well as making it possible to create special files (block and character devices, pipes and sockets), symbolic links (file names pointing to another files accessible locally, not necessarily on LizardFS) and hard links (different names of files which refer to the same data on LizardFS). Access to the file system can be limited based on IP address and/or password.

Distinctive features of LizardFS are:

  • higher reliability (data can be stored in several copies on separate computers)
  • dynamically expanding disk space by attaching new computers/disks
  • possibility of storing deleted files for a defined period of time (“trash bin” service on a file system level)
  • possibility of creating snapshot of a file, which means a coherent copy of the whole file, even while the file is being written to.

ARCHITECTURE

A LizardFS installation consists of five types of machines:

master metadata server (or ‘the master’)
a managing server - single computer managing the whole filesystem, storing metadata for every file (information on size, attributes and file localisation(s), including all information about non-regular files, i.e. directories, sockets, pipes and devices.
metadata server shadows (or ‘the shadow master’)
almost identical to the master, there can be any number of those, they work as master metadata server backup and they are ready for immediate deployment as the new master in case of current master failure.
data servers (or ‘the chunkservers’)
any number of commodity servers storing files data and replicating it among themselves (if a certain file is supposed to exist in more than one copy.
metadata backup servers (or ‘the metaloggers’)
any number of servers, all of which store metadata changelogs and periodically downloading base metadata file; it’s easy to run the mfsmaster process on such a machine if the primary master stops working.
client computers referring to LizardFS stored files (or ‘the clients’)
any number of machines with working mfsmount process that communicates with the managing server to receive and modify file information and with the chunkservers to exchange actual file data.

Metadata is stored in the memory of the managing server and is simultaneously being saved to disk (as a periodically updated binary file and immediately updated incremental logs). The main binary file as well as the logs are replicated to the metaloggers (if present).

File data is divided into fragments (chunks) of a maximum size of 64MB each which are stored as files on selected disks on the data servers (chunkservers). Each chunk is saved on different computers in a number of copies equal to a “goal” for the given file.

REPORTING BUGS

Report bugs to <contact@lizardfs.org>.

SEE ALSO

mfschunkserver(8), mfsmaster(8), mfsmetalogger(8), mfsmount(1), lizardfs(1), lizardfs-admin(8)