[rescue] Moving Sun servers?

Mr Ian Primus ian_primus at yahoo.com
Fri Apr 29 08:38:46 CDT 2011

--- On Fri, 4/29/11, Mike Loewen <mloewen at cpumagic.scol.pa.us> wrote:

>    Back in the '80s, I remember people
> telling me that after a hard drive had been running in one
> orientation for a long time, it was unwise to turn the
> system so the drive was in a different orientation. 
> Was there any truth to this, or was it just an urban
> myth?  Something about the bearings, as I recall.

This is actually true... with stepper positioned MFM hard drives. Drives like the venerable ST-225. Those had stepper motors and were low level formatted by the user. The stepper motor doesn't know where the tracks are, it just makes a step, and the drive formats the track, make anoter step, etc. Modern drives are voice coil positioned. The servo information for telling the mechanism where the tracks are is factory recorded on the drive. The positioner uses this data to find tracks - not by counting from a zero point.

So, if you had a stepper positioned drive up on end, and formatted/used it that way, and then you lay the drive flat... it might not be readable. Wear  changes the tolerances of the stepper, and "three steps from zero" was one place when gravity was pulling on the stepper sideways, and a slightly different place when the drive is laying flat.

This only affects worn/well used drives. It's pretty rare for it to be a problem. But I *have* seen this happen. And it will NOT happen with any voice coil positioned drive, which is pretty much all of them. Only old MFM, very early SCSI, and perhaps an 8 bit IDE drive or two are actually stepper positioned.


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