Next: Data Recovery
Up: Implementation Overview
Previous: Metadata Backup and the
The I/O trace of scientific applications shows a frequent pattern
that multiple clients concurrently access the same
files [17]. In CEFT-PVFS, we employ an centralized
byte-range locking mechanism to support the multiple-reader
single-writer semantics. When the metadata server receives a write
request, it looks at the desired portion of the destination file
and checks whether this portion has already been locked by any
other clients. If nobody locks this portion, the metadata will
issue an write-lock to the client to permit the write access.
Multiple read-locks can be issued to different read-only requests
as long as no conflicting write-lock exists. Deadlock is avoided
by using a two-phased locking, in which all locking operations in
a transaction precede the first unlock operation [18].
To reduce the overhead of locking, after the clients are granted
the access, they continue to hold this access grant for a short
period of time in a hope to save the negotiation with the metadata
server for the immediate accesses of the same data. This access
grant is revoked by the metadata server before the short period
expires if other clients are waiting. The centralized management
of locking certainly limits the parallelism of I/O operations.
However, as discussed in Section V, the metadata
server is not likely the bottleneck under our measurements.
Next: Data Recovery
Up: Implementation Overview
Previous: Metadata Backup and the
Yifeng Zhu
2003-10-16