>
> On 6 Feb 1996 17:27:10 EST, Paul Zarnowski wrote:
>
> > I am somewhat concerned that ADSM will not be able to drive the DLT drives
> > at their rated speed.  At some point, I think database updates may become
> > the limiting factor.  We are using regular fast scsi-2 drives for our db
> > (barracudas from seagate).  We have not been able to drive our 8mm drives
> > at their rated performance, and I am not sure what the reason for this is.
>
> We have similar experiences with an RS/6000 580 not being able to keep up with
> 8mm drives.  We have not studied it, but believe it is mostly on small to
> medium files with more database work relative to the file data.  We see some
> delays from the disks (IBM 4.5GB fast/wide) and very heavy CPU usage,
> especially when several sessions and processes are running.  We are purchasing
> an upgrade to a 590 in hopes it will help.
>
> The delays are compounded by the 8mm drive having to backspace when the CPU
> can't pump out data fast enough.  I have heard this is less of a problem with
> DLT or 3590, but have nothing to verify this.
[snipped]
>
>          Mike (Not ADSM Support) Knight
>

   The backspacing you refer to is due to the 8mm (and 4mm for that matter)
being helical scan technologies while the DLT and 34x0/3590 are linear
technologies.  Writing to tape in a start and stop mode which is what ADSM
seems to do, due to the database updates taking place, is not conducive to
high throughput on the helical scan type drives.  These type drives work
similarly to your VCR.  You know that when you hit the 'play' button on your
VCR it takes a few seconds for it to begin playing, and if you hit 'stop' and
'play' again it does the same thing.  Writing to an 8mm tape drive in a
non-streaming (or start/stop/start/stop) mode acts very similar to a VCR, it
just takes awhile to start up after each stop.  The linear type tape drives
are not as affected by this type of data input.  They can start and stop much
faster.  Basic but that's it in a nutshell.

Rich Campbell