sasaki@HARVARD.HARVARD.EDU (06/15/87)
GVGVGVGVGVGVGVGVGVGVGVGVGVGVGVGVGVGVGVGVGVGVGVGVGV From: sasaki@harvard.harvard.edu (Marty Sasaki) To: info-vax@kl.sri.com Subject: Optical disk hardware for backup Return-Path: <@KL.SRI.Com:sasaki@harvard.harvard.edu> Redistributed: XeroxVAXInterest^.x Received: from KL.SRI.Com by Xerox.COM ; 12 JUN 87 08:36:09 PDT Received: from harvard.harvard.edu by KL.SRI.COM with TCP; Thu 11 Jun 87 00:17:49-PDT Received: by harvard.harvard.edu; Thu, 11 Jun 87 03:17:41 EDT Received: by endor.HARVARD.EDU; Thu, 11 Jun 87 03:18:15 EDT Original-Date: Thu, 11 Jun 87 03:18:15 EDT GVGVGVGVGVGVGVGVGVGVGVGVGVGVGVGVGVGVGVGVGVGVGVGVGV 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