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Chapter 2 HPSS Planning
138 September 2002 HPSS Installation Guide
Release 4.5, Revision 2
application, a number of the disks can be grouped together in a striped Storage Class to allow each
disk to transfer data in parallel to achieve improved data transfer rates. If after forming the stripe
group, the I/O or processor bandwidth of a single machine becomes the limiting factor, the devices
can be distributed among a number of machines, alleviating the limitation of a single machine.
If the client machine or single network between the client and HPSS becomes the limiting factor,
HPSS supports transferring data to or from multiple client machines, potentially using multiple
physical networks, in parallel, to bypass those potential bottlenecks.
During system planning, consideration should be given to the number and data rates of the
devices, machine I/O bandwidth, network bandwidth, and client machine bandwidth to attempt
to determine a configuration that will maximize HPSS performance given an anticipated client
work load.
2.11.5 Configuration
The configuration of the HPSS storage resources (see Section 2.8.6) is also an important factor in
overall HPSS performance, as well as how well the configuration of those resources matches the
client data access patterns.
For example, if a site provides access to standard FTP clients and allows those clients to write data
directly to tape, the buffer size used by the FTP server and the virtual volume block size defined for
the Storage Class being written to will have a significant impact. If the buffer size used by the FTP
server is not a multiple of the virtual volume block size, each buffer written will result in a distinct
storage segment on the tape. This will cause additional metadata to be stored in the system and
extra synchronization processing of the tape. (If the buffer size is a multiple of the virtual volume
block size, each write will continue to append to the same storage segment as the previous write.
This will continue until the final write for the file, which will usually end the segment, thus
reducing the amount of metadata generated and media processing.)
2.11.6 FTP/PFTP
Data transfers performed using the standard FTP interface are primarily affected by the buffer size
used by the FTP Daemon. The buffer size canbe configured as described in Section 7.3: FTP Daemon
Configuration (page 422). It should be a multiple of the storage segment size, if possible. If not, it
should be, at least, a multiple of the virtual volume block size. If the buffer size is too small, the FTP
Daemon will need to issue a large number of individual read or write requests; however, if the
buffer size is too large, the FTP Daemon will require a large amount of memory, which may cause
additional paging activity on the system.
The size of the FTP Daemon buffer is extremely important if the FTP clients write files directly to a
tape storage class, as described in Section 2.11.5.
Parallel FTP (PFTP) can be used to move data using TCP/IP.
Note that the PFTP data transfer commands (e.g., pput and pget) are not influenced by the FTP
Daemon buffer size because the data flows directly between the client and Movers.
Note that PFTP clients that use the standard FTP data transfer commands (e.g., put and get) have
the same performance considerations as standard FTP clients as described in Section 2.11.6.