[Info-vax] Question about IDE disks

[H Vlems]

On Dec 23, 7:36 pm, JF Mezei <jfmezei.spam... at vaxination.ca> wrote:
> Just as a sanity check.
>
> With proprietary disks such as RA and DSSI, VMS had very good control
> and more importantly notification of errors which would then show up in
> the SHOW DEVICE output.
>
> There was a phase in time where Alphas supported el-cheapo (made for
> Windows PC)   IDE (now called ATA) disks.  (models such as DS10/DS10L
> for instance).
>
> Do those drives (and IDE protocol) give VMS the same level of
> notification as previous generation of disk protocols ? Or do they
> perform their own internal disk maintenance without bothering the OS ?
>
> In other words, if an IDE disk is starting to make weird noises, does an
> error count of 0 on the SHOW DEV provide some indication that the noises
> have not resulted in problems with actual disk operation, or could the
> disk already be seriously sick and just not reporting its problems to
> the OS ?

JF,
from the way Seagate issues model numbers, I'd assume that the HDA and
the drive electronics are two distinct products.
Drive electronics (again, just my guess) are part drive specific and
part depending on the connecting bus.
A Seagate model looks like this:
  ST <geometry><capacity><connection type>
Where:
  <geometry> is a single digit that tells you about the width and
heigth of a drive. E.g. 1 is a 3.5" drive disk, approx. 1.5"high and 3
is a 1"high drive
  <capacity> is either in kB or in MB, depending on the age of the
drive in four or five digits
  <connection> one or two letters specify the interface. E.g. N is 50
pin SCSI-2, A is IDE and WC is SCSI-SCA
So an ST32550WC is a 3.5" disk, 1" high with a storage capacity of 2.5
GB (formatted, VMS will see approx. 2.1 GB nett storage).
Now many drives were available as families. Example the ST34501 came
in 5 different interface versions N/W/WC/WD/DC.
Which led me to believe that Seagate designs an HDA and slaps a pcb on
it fitted with a specific interface.
Now in this example (The ST34501 is from 1997) the "A" is missing.
Until a couple of years ago SCSI drives had larger capacity than IDE
drives and very likely their HDA's were built and designed for 24x7
usage.
Apparently that difference no longer mattered for the production of
the HDA, hardware MTBF figures just went up, and an HDA was used for
SCSI and IDE.
Today SCSI lags behind, 300 GB is the maximum capacity for SCSI while
IDE is available at 500 GB (perhaps even bigger).
I do not know about the differences between serial SCSI and serial ATA
(SAS and SATA) but I'm willing to propose that these drives share the
same HDA's.

IDE drives (parallel ATA) have a facility called SMART which allowed
the drive to inform the OS about the shape it was in. I don't know
whether VMS can interpret the data but it surely is available. DEC
provided utilities to extract data from DSSI and SCSI devices so
perhaps it is possible to write a similar tool to inspect IDE drive
logic?
Hans