Chapter 2 HPSS PlanningHPSS Installation Guide September 2002 139Release 4.5, Revision 2Parallel transfers move the data between the Mover and the end-client processes bypassing theHPSS FTPD. Customers should be educated to use the parallel functions rather than the non-parallel functions. NOTE: ASCII transfers are not supported by the parallel functions and the non-parallel functions will need to be specified for ASCII transfers. ASCII transfers are NOT typicallyrequired; but the end-customer should familiarize themselves with the particulars.Parallel transfers should be optimized so that the Class of Service (COS), Media Stripe Widths,Network Stripe Widths, and Parallel Block Sizes are consistent with each other. E.g., using aNetwork Stripe Width of 4 with a Media Width of 2 may result in poorer performance than if bothspecifications are equal! Specifying a Network Stripe Width of 4 where there is only one networkinterface may not provide any improvement over a lower Network Stripe Width (2) if thebandwidth of the network is (over-)filled by a 4-way stripe.Non-parallel transfers occur via a “stage and forward” approach (Device <==> Mover <==> HPSSFTP Daemon <==> FTP Client.) It is recommended that the “–h” option be specified on thehpss_pftpd and that the “hpss_option HOST hostname” be specified in the ftpaccess file if the FTPDaemon system has multiple interfaces. The hostname should refer to the highest speed interfaceavailable for transmission of data between the FTP Daemon and HPSS Movers. NOTE: thisinterface MUST be available to all client systems that contact the FTP Daemon.Where reasonable, the standard FTP ports should be modified to something other than 20/21 onthe system acting as the HPSS FTP Daemon. The HPSS FTP Daemon should be set to use the 20/21 ports by default. This reduces the problem of requiring the end-customer from needing to knowwhich port to use for transfers to HPSS. In conjunction with this, it is highly recommended that the{ftpbanner} file be used with an appropriate message to provide information to the end-customerthat they are accessing HPSS as opposed to a standard system.2.11.7 Client APIThe Client API provides the capability to perform data transfer of any size (the size beingparameters supplied by the client to the read and write interfaces). The size of the data transfers canhave a significant impact on the performance of HPSS. In general, larger transfers will generate lessoverhead than a series of smaller transfers for the same total amount of data.The size of the transfers is extremely important because the clients may write files directly to a tapestorage class, as described in Section 2.11.5.2.11.8 Name ServerMinor performance degradations may be seen when the Name Server is processing path nameswith a large number of components, listing directories containing entries with long (greater than 23characters) names, servicing requests for objects which have a large (greater than 4) number ofObject ACL entries, and servicing requests for objects which have Initial Container/Initial ObjectACL entries.2.11.9 Location ServerThe Location Policy defined for a site generally determines how the Location Server will performand how it will impact the rest of the HPSS system. View the help for the fields on this screen todetermine if the values need to be changed. The default policy values are adequate for the majority
