Overview of the Gfarm filesystem
About the Gfarm filesystem
The Gfarm filesystem is a distributed filesystem consisting of the local
storage of commodity PCs. Many PCs in a local area network, compute
nodes in a single cluster, multiple clusters in wide area, comprise a
large-scale, high-performance shared network filesystem.
The Gfarm filesystem solves performance and reliability problems in
NFS and AFS by means of multiple file replicas. It not only prevents
performance degradation due to access concentration, but also supports
fault tolerance and disaster recovery.
A unique feature of Gfarm is that each filesystem node is also a client
of the Gfarm filesystem. Distributed access by filesystem nodes
realizes super-scalable I/O performance.
For detailed information about the Grid Datafarm architecture and
Gfarm file system, refer to the following papers.
 Osamu Tatebe, Youhei Morita, Satoshi Matsuoka, Noriyuki Soda,
"Grid Datafarm Architecture for Petascale Data Intensive Computing,"
Proceedings of the 2nd IEEE/ACM International Symposium on Cluster
Computing and the Grid (CCGrid 2002),
IEEE, pp.102-110, 2002
 Osamu Tatebe, Noriyuki Soda, Youhei Morita, Satoshi Matsuoka,
"Gfarm v2: A Grid file system that supports high-performance
distributed and parallel data computing"
Proceedings of the 2004 Computing in High Energy and Nuclear
Physics (CHEP04), 2004
How to access Gfarm
There are two methods that can be used to access the Gfarm filesystem:
- Using Gfarm commands and Gfarm native file I/O APIs
You can use Gfarm specific features like file replication,
filesystem node management, etc., via this method.
- Using GfarmFS-FUSE (gfarm2fs)
You can actually mount the Gfarm filesystem from Linux clients
by using FUSE (http://fuse.sourceforge.net/).
Unlike the other methods, this one is completely transparent from your
Host types that make up the Gfarm system
A Gfarm system consists of the following kinds of nodes:
- Client node
A terminal node for users.
- Filesystem node
Filesystem nodes provide data storage and CPUs for the Gfarm system.
On each filesystem node, the Gfarm filesystem daemon, called gfsd,
is running to facilitate remote file operations and access control
in the Gfarm filesystem, as well as to provide user authentication, file
replication, node resource status monitoring, and control.
- Metadata server node
A metadata server node manages Gfarm filesystem metadata. On the
metadata server node, a Gfarm filesystem metaserver (gfmd), and a
backend database server such as an LDAP server (slapd) or a
PostgreSQL server (postmaster) are running.
The three types of nodes just introduced are not necessarily different
i.e., you can use the same host for the above purposes, if the number of
available hosts are limited.
Physically, each file is replicated and dispersed across the disks of the
filesystem nodes, and they will be accessed in parallel.
Structure of the Gfarm software
The Gfarm filesystem consists of the following software:
- The libgfarm.a library
A library that implements Gfarm APIs, including Gfarm file access,
file replication, and file-affinity process scheduling.
- gfmd - the Gfarm filesystem metadata server
A metadata server for the Gfarm file system that runs on a metadata
server node. It manages directory structure, file information,
replica catalog, user/group information, and host information.
Gfmd keeps the metadata in memory, but it stored a backend databse
such as PostgreSQL server or OpenLDAP server, on background.
- gfsd - the Gfarm filesystem daemon
An I/O daemon for the Gfarm filesystem that runs on every
filesystem node, which provides remote file operations with access
control, as well as user authentication, file replication, and node
resource status monitoring.
- Gfarm command tools
Gfarm command tools consist of filesystem commands such as gfls,
gfrm, gfwhere and gfrep; a filesystem node management tool,
gfhost; file management tools such as gfreg and gfexport; session
key management tools, such as gfkey.
gfmd and gfsd support the following three authentication methods.
Please read the security section in Gfarm-FAQ.en, too.
This uses a shared key in the ~/.gfarm_shared_key file which will be
generated automatically by the Gfarm software.
This is suitable for an environment that is protected by a firewall.
This authentication method is easy to use in an environment which
shares users' home directories via NFS.
This is the GSI -- Grid Security Infrastructure -- method, and it uses
public key authentication, which is based on a PKI-style certificate.
This method encrypts network communication, and is suitable for
use over the Internet.
Please read the following page provided by the Globus project for details:
This method uses GSI for its authentication, but switches to a plain
TCP connection after the authentication is completed.
This method is suitable for an environment that is protected
by a firewall.