SCSI change requires a reboot?

[Brian Abdallah_2]

Recently I changed a terminator on a HP system.
Model 9000/735. It has 7 drives each terminated individually. I pulled out the drive
bay, changed the terminator, ran ioscan.
No errors occurred.
Should I have rebooted the box? Someone said I
should have as I could have corrupted the data.
But, the drive was removed when I changed
terminators so no data could be damaged.
Please advise as to whether, reboots are required when changing SCSI devices, terminators, etc? or ... a ioscan command will
suffice

[A. Clay Stephenson]

The answer is that it depends. The safe answer is to say that only devices designed to be hot-plug should be removed 'on the fly'. In most cases, you can remove and install devices on a relatively quiet SCSI bus and no harm is done. Removing terminators, however, is an especially bad idea. That definitely leaves the bus in an unexpected condition. The terminator serves the same purpose that a 'wall of dough' would do for a rubber ball. It damps the standing waves on the bus. The proper and safe answer is that you should power down all equipment (unless specifically designed to be hot-plag) and then make the changes but most of the time no harm is done.

[steven Burgess_2]

Hi

If you ask any engineer he will advise to power off the server. (I would also) as you are always at risk if you short a device or card. You wouldn't change a light bulb with the light switch on would you ?

Steve

[Michael Lampi]

First, absolutely none of the disk drives should be terminated, with the possible exception of the last drive at the end of the SCSI bus furthest from the 735. Ideally, the only terminator would be an external on at the end of the cable coming from the last drive.

Second, you should most definitely have shut down the OS and powered the system off before pulling out the drive bay. The shock and vibration of removing the tray can easily damage spinning media, not to mention the spikes in the power lines causing havoc, and not mentioning the possibility that data written to the drive(s) might still be cached in RAM on the drives and not actually on the media.

Now if you have a "hot plug" chassis for a drive, then it is possible to install and remove a drive as you suggest - IF YOU ARE VERY CAREFUL ABOUT IT. That is, you must be sure to dismount the drive, wait until the drive access light has not blinked for at least a minute, and then power down the drive - waiting at least 20 seconds for the drive to spin down.

On the other hand, if you have a "lab" computer in which you either 1) don't care so much about your data integrity or 2) have an extra unused SCSI bus, then you can pretty much play with the (preferably) unused SCSI bus to your heart's content. ioscan and insf are about all you need. I do this sort of thing all the time, and have lost only one SCSI bus in about 10 years of playing, er, working.