[Info-vax] Databases versus RMS

[abrsvc]

On Friday, April 20, 2012 12:38:59 PM UTC-4, glen herrmannsfeldt wrote:
> abrsvc <dansabrservices at yahoo.com> wrote:
> > On Friday, April 20, 2012 11:44:36 AM UTC-4, Ken Fairfield wrote:
> 
> (snip)
> >> The first Intel fab I worked at was using DEC SSD's for the "hot"
> >> database files.  This was VAXcluster (7800's IIRC).  I'm pretty
> >> sure the SSD's were in SSB's.  I *know* that these SSD's had
> >> rotating disks in the same package (SSB) for non-volatile storage.
> >> I don't recall for sure, but I *think* they had (small?) batteries 
> >> as well so the memory could be written to the disks in the event of
> >> a power failure.
>  
> >> What I found interesting is that, by the time I got there, these
> >> SSD's were suffering a fairly high failure rate.  And it was 
> >> universally the rotating disks that were failing. ;-p  OTOH, by
> >> the time they were failing, you couldn't buy such things anymore
> >> (from DEC/Compaq).
> 
> (snip)
> > The disks were there for backing up the memory in the event of 
> > a power failure.  There was at least one attempt to have the 
> > drives in "standby" or not spinning, but the spinup time was 
> > too long for reliable backups.  Thus, the mode was to keep the 
> > drives spinning and ready for data transfer.  
> 
> I wonder if just spinning, and rarely seeking, is not so good
> for the drives. The actuator might take a set in one position,
> and then not move when it needs to.
> 
> -- glen

In the days of the stepper motor, that was a problem.  In more modern drives, the actuator arm is driven by a coil so no real friction or contact points.  Usually it wouldbe in the "home" position as well  The biggest problem was the current required to start the unit spinning.  With the drives spinning, the amount of power required to keep it that way is significantly less than to start it spinning.  This allowed the total power required to both spin and record the data to be much less in both capacity and endurance.