IBM s/390 SCSI adapter for the ThinkPad, Disk fragmentation, Backup and restore considerations

￿Extensive testing would be necessary to verify PCI bus functions with the FSI adapter cards in this environment. This has not been done.

5.13SCSI adapter for the ThinkPad

Potentially, one might provide an SCSI interface to the ThinkPad and connect external SCSI tape drives. The supported ThinkPad models do not have this capability, but there are third-party PCMCIA cards that might be used. We did not attempt to use a SCSI PCMCIA adapter during our projects. If you require this function, we suggest you contact your business partner or FSI.

5.14 Disk fragmentation

The raw disks used with UnixWare-based EFS to hold emulated S/390 volumes have a unique advantage. A raw disk is contiguous space on a hard disk drive. Linux file systems do not necessarily provide contiguous space for Linux files. After a Linux file system has been used for normal file creation, deletion, and general operations, it would be unusual for a large file (such as an emulated S/390 volume) to be created in contiguous space in the file system.

FLEX-ES performance benefits from contiguous disk space for an emulated volume. FLEX-ES typically performs Linux disk operations in units of a full track for the emulated volume. For an emulated 3390, this would be 57 KB. If the data is fragmented in different areas of the Linux file system, the I/O operation takes longer.

The standard Red Hat 7.1 distribution does not contain a standard defrag command. Several defrag-type utilities are available from various Web sources; we did not have the time or resources to thoroughly test any of these and did not use them.

We took the following approach:

￿A file system performs contiguous file creation when the file system is new.

￿We placed S/390 volumes in separate file systems (/s390 and /s391).

￿Generally, we did not place anything else in these file systems. (There are always exceptions, of course, and several of our backup/restore methods used files in these file systems.)

￿The slight fragmentation caused by, for example, deleting three (discontiguous) 3390-1 volumes and creating a 3390-3 volume is not significant.

More work is needed to understand the effects of fragmentation on FLEX-ES operation and to document techniques to avoid problems in this area.

5.15 Backup and restore considerations

Since a typical12 ThinkPad/EFS cannot directly connect to tape drives, the backup options are more limited than for a Netfinity/EFS system. Still, backing up and restoring S/390 data has interesting variations. The most basic element involved is where to store your backup data. There are several options:

12A ThinkPad/EFS system might use remote FLEX-ESresources to connect to a machine that does have attached tape drives. This should work (although we did not try it), but cannot be considered a typical ThinkPad/EFS environment.

Chapter 5. Additional Topics 53