QFS is a SAN-based shared
filesystem which is optimized for performance and scalability. It allows
multiple nodes to simultaneously read and write to the same filesystem,
or even to the same file. On SciClone, QFS is hosted on the front-end
fileserver nodes, and then exported via NFS to the entire cluster.
QFS is configured on
SciClone to prevent multiple hosts from writing to the same file at
the same time (mh_write option is disabled, which is the default
behavior). This provides filesystem semantics that are similar to the
POSIX standard. If you have an application which would benefit from
simultaneous writes to a single file, and also takes into account QFS
consistency limitations such as page-aligned I/O, please contact us
at sciclone@compsci.wm.edu.
For more details about the behavior of multiple writes, see Chapter
5 in the QFS/SAM-FS
File System Administration Guide. Note that simultaneous reads from
the same file and simultaneous writes to different files are always
allowed.
QFS is optimized for
high-speed serial access to very large files. Small files are stored
inefficiently, and can waste substantial amounts of disk space. In particular,
QFS filesystems are not recommended for storing source code, or for
large collections of small data files. As a rule of thumb, files smaller
than about 1 MB should be stored in UFS filesystems (i.e., /sciclone/homeXX,
/sciclone/scrXX, or /local/scr). For more information about
filesystems, consult the SciClone
Users's Guide.
