[comp.os.vms] Optical disk hardware for backup

sasaki@HARVARD.HARVARD.EDU (06/15/87)

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From: sasaki@harvard.harvard.edu (Marty Sasaki)
To: info-vax@kl.sri.com
Subject: Optical disk hardware for backup
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We use several different types of write once optical disks in the
things we do, and we OEM several drive/controller configurations for
use with the archiver that we sell. Everything is off-the-shelf.

All of the drives are SCSI based so it isn't too difficult to
interface with the drives. Device drivers tend to be very similar (the
driver we use serves 6 devices on two controllers with small changes
between the different combinations).

A lot of people are using/selling the Hitachi 12 inch drive. This
holds 1.3 gigabytes per side (you flip the things over, like two sided
floppies). Hitachi makes a jukebox which holds 32 platters and up to
two players. Platters are about $300 (in large quantities).

We also use Optimem drives which also use 12 inch media, but these are
not compatible with Hitachi. They hold 1,000,000 1024 byte blocks per
side. Media is about the same cost as Hitachi.

Hitachi drive with a U.S. Design SCSI controller cost around $15000.
Qualitatively the drives are about the speed of the RD-class drives,
maybe a little slower.

At the AIIM show Kodak showed a 14 inch platter/drive/jukebox. They
are still in the development phase (the unit was a prototype) so the
capacity is still not firm, but looks to be at least 6 gigabytes per
side and will probably be around 20 gigabytes in the future. The
jukebox will hold up to 4 players and around 128 platters. As I say,
they did show a working prototype, but will probably change things
over time. Kodak made no commitments, but they are obviously serious
about this thing.

We have also started to experiment with Maxtor's 5 inch (CD size)
drive. It is the same size as a TK-50, RD-53, etc., fits nicely into a
uVAX cabinet. The default capacity, using 2048 byte sectors, is just
over 400 meg per side. Larger sectors (switch selectable) increase the
capacity. The really good news about this drive is that it costs less
than $3000 (quantity one) and the media will probably drop to around
$100 a platter. The Maxtor runs faster than floppies, but is
*definitely* slower than RD-class drives.

Currently WORM is a little expensive for backup. This is because tape
can be re-used and most folks cycle through at least part of their
tapes. Optical really wins big for permanent storage (archiving, long
backups, etc.) where media cost is roughly the same as tape (the CD
size media will eventually be cheaper than tape). Imagine several
hundred 2400 foot tapes worth of data on a multi-album box (assuming
you leave the disks in the cartridges, you can remove them and then
you get a single album's width). No more changing tape reels.

No one really knows how long the data stays good, but is at least 10's
of years.

Software is still an issue and there are many approaches to using the
devices. Device drivers aren't much of a problem since most of the
drives connect to SCSI. Emulex makes a controller that uses the
standard dudriver.

Several companies use driver software to make the optical disks look
like tape drives. You can use backup, copy or whatever to put stuff on
to these drives. This seems like a reasonable approach and is simple
and straightforward.

Another approach is to make the disk appear just like a magnetic disk.
Usually this means caching the index file and directory files on
magnetic disk and writing this out on dismount. This means wasting
some of the storage on the optical disk since you have to fix up
things like bitmaps every time you dismount the disk and you only get
to write a block once. This is a very easy way to handle the disks.
----------------
  Marty Sasaki                          uucp:   harvard!sasaki
  Ziff Davis Technical Information Co.  arpa:   sasaki@harvard.harvard.edu
  80 Blanchard Road                     bitnet: sasaki@harvunxh
  Burlington, MA 01803                  phone:  617-273-5500