Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!uunet!seismo!mcvax!ukc!stc!ist!micas!jvs From: jvs@micas.UUCP (Jo stockley) Newsgroups: comp.periphs,comp.unix.wizards Subject: Re: Filesystem/archive formats for WORM optical disks Message-ID: <531@micas.UUCP> Date: Mon, 17-Aug-87 05:33:36 EDT Article-I.D.: micas.531 Posted: Mon Aug 17 05:33:36 1987 Date-Received: Sat, 22-Aug-87 01:44:31 EDT References: <212@casemo.UUCP> Organization: Nodecrest Ltd., Byfleet, England Lines: 86 Xref: mnetor comp.periphs:535 comp.unix.wizards:3771 in article <212@casemo.UUCP>, brian@casemo.UUCP (Brian Cuthie ) says: > Summary: WORM disk structures > Xref: micas comp.periphs:175 comp.unix.wizards:1846 > Xpath: icdoc ivax > > There are two major problems when using optical WORM (Write Once Read Many) > drives. First, the block size is usually 1024 bytes instead of the usual 512. > Second, when a block is written, it's ECC is also written. Since the media > is Write Once, it is impossible to simulate a 512 byte/block file system > using the usual read block, update the half you want, write block. Note, > that this is impossible even if the half in question has never been written; > it's ECC has. > > The only reasonably transparent sollution I have seen is to have the > controller > map the directory part of the filesystem to a magnetic drive and the data > portion to the Optical drive. Thus part of the optical drive has been > mapped (or overlayed) with magnetic media. Since this is done by > the controller > all the operating system must do is write data in even numbers of blocks and > limit directory blocks to the portion of the WORM drive that has been mapped > to magnetic media. When the data area (the optical drive) is full, > the magnetic > disk is copied to the area on the optical it had previously overlayed. This > freezes the filesystem onto the optical platter. Note that the magnetic > drive only needs to be as large as the directory area of the WORM filesystem. We have recently evaluated a WORM subsystem consisting of a OSI WORM drive (I think there's some link with CDC the OSI drive) and a software package called DOROFILE which is produced by a French company called DOROTECH. To quote from the release 2.2 manual: " ... DOROFILE has been written with three major objectives: - To stay in complete accordancewith all UNIX concepts concerning files and directories. - To offer the same user and programmer's interfaces as UNIX does. - To use the optical disc to the most of it's possibilities. ...." They go on to say that " Each disk is totally independant of other storage devices (unlike some WORM file systems where part of the disk indexing is stored in a file on a seperate magnetic disk). " They have also implemented version numbers for files on the optical disk which is of great use to us. The commands are like UNIX only with an 'o' in front, e.g. ols, ocd, ocp etc. The software supports several WORM drives including CDC-OSI, Optimem and GIGADISC. Well it works and we are going to use it in our imaging system on the Sun as we have not seen or heard of anything better. I don't know if it works on anything other than the Sun systems. The only drawback we have seen is that for some reason all the error messages come out in French, followed by a cryptic UNIX message. I trust they will change this at some point. A distributer in the UK is: Program Products Ltd. Tileman House, 131 Upper Richmond Road, London SW15 2TP Telephone: (+44) 01 785 3055 And a contact name is: John Slater. Make of this what you will. Jo. -- ------------- Jo. Stockley. (jvs@micas.uucp or ...!mcvax!ukc!micas!jvs) Nodecrest Computer Systems Ltd Byfleet, UK. Phone: +44 09323 40555