Karen,
In essence, Hein is correct. A while ago, a systems programmer at a site with which I was connected throught that the correct allocation minimum would be half a disk track (in those days approximately ten sectors).
When disk space ran low, an analyis showed that our actual file allocations were resulting in a breakage factor of approximately 30% (30% of our disk space was unusable because of the "last sector vs. last allocated sector" effect (a one block file used only a single block but allocated an entire cluster).
A secondary problem was backup capabilities (or lack thereof). Pre-BACKUP, there was no good tool to restoring a disk with a different cluster factor.
The option of simply purchasing an additional disk drive was out of the question. Then current prices meant that that option was, in relative terms, the equivalent of a good portion of a man-year, and totally out of the question.
Researching the problem, I was able to determine (for an ODS-2 disk) the necessary surgery was feasible. Ensuring that the data was backed up, I dismounted the disk, and sucessfully made the changes. (I was also not a cowboy about it, I did take the precaution of checking with one of my Engineering contacts, Hein can take a good guess as to whom, but I will not identify). My contact noted that there was an even shorter way to accomplish what I was doing.
Was it the computer equivalent of neurosurgery, probably. But neurosurgery is reasonably safe, when done with the correct preparation, testing, and care.
Would I (and could I) do it again in the same or a similar situation, yes. Do I recommend it as a general procedure, NO. The actual downtime to do this change is measured in seconds, and does not require a reboot of the system or cluster. Properly prepared, the operation is safe.
- Bob Gezelter,
http://www.rlgsc.com
