Tim,
Regarding Uwe's remark:
"They (DEC) for a long time disclaimed the need for defragmentation until they provided defrag hooks in the XQP. "
Well, it was more like every time a new version of VMS (as it was then) was released, lots of disks were broken because the defrag makers had made invalid assumptions about how the XQP worked. The defrag hooks were implemented to protect customers. A corporate defragger was also created because (in a rare flash of marketing sanity!) someone realised there was a market for it and DEC could make some money.
Some of us still disclaim the need for defragging disks. It should be possible with a small investement in planning and management to avoid the need to defrag files, simply by preventing them from fragmenting in the first place. Sometimes it's as simple as setting reasonable extend sizes.
It should also be realised that the OpenVMS file system needs to be VERY fragmented before there are any serious performance issues, so a little fragmentation isn't a problem. Indeed, for some workloads, a fragmented disk is GOOD (for example, many small files being created and deleted).
Further realise that OpenVMS is a multiuser operating system, so there are many processes using the disk at the same time. Thus, the one place you can be almost certain a disk head will NOT be is where you left it! A lot of the myths about keeping disks defragged is from single user systems and less sophisticated file systems.
Before spending big bucks on a license for a defragger, please find out what (if anything!) is the REAL problem. Not only can you save on the cost of the software, you can also save the resources need to run the defragger.
A crucible of informative mistakes
