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CEFT-PVFS maintains two metadata structures, system metadata and
file metadata. The system metadata indicates the dead or live
status of the data servers. When one data server is down, all I/O
access will be redirected to its mirror server. Currently, a data
server is simply thought to be down if the metadata server does
not receive the periodic ``heartbeat'' message from this data
server within a certain amount of time. The file metadata
describes the striping information, the data mirroring status and
other conventional file information, such as ownership, access
mode, and last access time, etc. Like UNIX file systems, the
access authorization is implemented by checking the ownership and
access mode. Table I gives a metadata example
in CEFT-PVFS with 8 data servers in either storage group.
Table I:
Sample Metadata in CEFT-PVFS
striping information |
|
3 |
|
65536 bytes |
|
1, 2, 7 |
data duplication status |
|
3, 3, 3 |
others |
|
213 |
|
501 |
|
rwx-r-r |
|
786432 bytes |
|
Wed Jan 22 09:00:10 2003 |
|
|
The striping information is described by the stripe width, the
stride block size and the data location. The , an array
of size , records the data server indices on which
the data is striped. In this example, the file is striped across 3
data servers, i.e., Node 1, 2 and 7, with a striping block size of
64KB. While the is given by clients, the values of
are assigned by the metadata server to approximately
balance the disk space utilization on each data server.
The , an array of size , describes the
mirroring status between two groups of mirroring servers that a
file is striped on. More precisely, it is defined according to the
status of data blocks, shown as follows.
where
.
Next: Metadata Backup and the
Up: Implementation Overview
Previous: Design of CEFT-PVFS
Yifeng Zhu
2003-10-16