nessus@athena.mit.edu (Doug Alan) (03/25/88)
This article describes my current solution to cheap disk space on a
VAXstation. Much of it is also relevant to any computer which can use
SCSI or ESDI disk drives, such as Suns, Macintoshes, etc. In a
previous article I mentioned $1939 for 320 Mbytes (formatted) of disk
storage. This figure would come by purchasing a Maxtor XT-3380, which
is a 5.25 inch SCSI hard drive. It is available from Anthem
Electronics (617-657-5170) in Massachusetts, and probably any other
Maxtor distributor. This is for the price of the drive alone for use
as an internal drive and does not include a power supply, cables, or a
box. For use in a VAXstation in a BA123 box, however, there is no
need for a power supply or a box, as the BA123 has enough power and
mounting shelves for up to five internal drives. For the VAXstation,
one *will* have to purchase a slide plate to mount on the bottom of
the drive and purchase or build a cable. The slide plate (with
grounding clip) costs $19 ($5 for the plastic structural component of
the slide plate and $14 for the grounding clip). You can build a
cable for about $20. This brings the total price to $1978.
There is a small problem here, however. A VAXstation comes with an
RQDX controller, which doesn't work with SCSI drives. I'm told that
the RQDX controllers use something called "ST506". Is this true? The
cables for DEC RD5x drives look just like ESDI cables, but they're not
compatible with ESDI? Does anyone know if inexpensive high capacity
ST506 disk drives are available?
In any case, this is not a problem for us, since we have already
replaced the RQDX3 controllers in our VAXstations with SDC-RQD11-EC
controllers from Sigma Information Systems (714-632-0474). The Sigma
controller is a Qbus controller that controls up to four ESDI disk
drives and emulates DEC's MSCP protocol. We are using ESDI disk
drives, not SCSI drives, but inexpensive ESDI Maxtor disk drives are
also available and, in addition, Sigma is coming out with a SCSI
version of this disk controller in the near future that will will
handle up to 7 disk drives and tape drives.
The Sigma disk controller is a very nice item. It has a 1 megabyte
RAM cache (we seem to be getting 25% cache hits with 4.3BSD+NFS), and
will do prefetching of disk sectors into the cache, cached
write-through, drive shadowing, staggered spin-up, etc., if you
configure it to do so. It does automatic, dynamic bad block
forwarding, so that the computer is always presented with perfect
media. The controller keeps statistics on cache hits, seeking
distances, bad block forwarding, soft errors, and it lets you examine
this information (and reset if you want to). It has nice firmware
called "Wombat" that lets you format the drive, exercise it, divide
the disk up to smaller logical disks, and set and examine the various
control parameters. Each drive formatted with Wombat can report
itself to Unix as whatever type of drive you want to say it is.
Wombat can be run from the console in standalone mode, or you can
actually connect a terminal to the disk controller itself. We got
these controllers for $1020 a piece, but we got a discount. $1500 is
probably a more typical price. The SCSI verion will be pretty
identical to this, except that it will not have such a huge RAM cache,
it will also emulate TMSCP for tape drives, it will control up to
seven devices, and it will be cheaper. The discounted price quoted to
us is $866.
Now it's time to back up and go back to disk drives. The Maxtor
XT-3380 is the cheapest Maxtor drive in dollars per megabyte, but the
XT-4380 is probably a better buy. The XT-3380 only has an average
seek time of 27 mSec, while the XT-4380 has an average seek time of 18
mSec and is a little bit larger. The XT-4380 holds 338 Mbytes
formated (384 unformated) and comes in two versions, the XT-4380S
(SCSI) and the XT-4380E (ESDI). The XT-4380S has a maximum transfer
rate of greater than 4.0 Mbytes/Sec compared to 1.5 Mbytes/Sec for the
XT-3380 and XT-4380E (ESDI can't handle any more than 10 Mhertz). The
Qbus can't keep up with 4.0 Mbytes/Sec, so on a VAXstation, it
probably makes little difference whether you get the ESDI version or
the SCSI version, but a Sun might be able to keep up with the
XT-4380S. The cheapest price I found for the XT-4380S is $2125 from
Storex in Massachusetts (with some bargaining, 617-769-3400), and the
cheapest price I found for the XT-4380E is $2125 from Anthem
Electronics (617-657-5170). Pioneer in Massachusetts (617-861-9200)
also had good prices.
As mentioned before, if you are going to want to hook up any of these
drives as an external drive (on a Sun or Macintosh, for example), you
will also have to purchase a power supply, box, and mounting
paraphilnalia. In any case, you will need cables. This stuff will
probably cost a couple hundred bucks.
|>ouglas /\lan
(or nessus@athena.mit.edu
nessus@mit-eddie.uucp)