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From: rbl@nitrex.UUCP
Newsgroups: comp.periphs,comp.unix.wizards
Subject: Re: Filesystem/archive formats for WORM optical disks
Message-ID: <516@nitrex.UUCP>
Date: Thu, 13-Aug-87 13:05:02 EDT
Article-I.D.: nitrex.516
Posted: Thu Aug 13 13:05:02 1987
Date-Received: Sat, 15-Aug-87 16:04:45 EDT
References: <1775@kontron.UUCP> <212@casemo.UUCP>
Reply-To: rbl@nitrex.UUCP ( Dr. Robin Lake )
Organization: The Standard Oil Co., Cleveland
Lines: 32
Xref: utgpu comp.periphs:469 comp.unix.wizards:3415
Summary: Try Optotech, Inc., Colorado Springs

In article <212@casemo.UUCP> brian@casemo.UUCP (Brian Cuthie ) writes:
>In article <1775@kontron.UUCP>, brad@kontron.UUCP (Brad Yearwood) writes:
>> Write-once-read-mostly optical disks, while promising very large storage
>> capacities economically and in a small space, do not fit well with
>> the types of file allocation and directory structures used on rewritable
>> magnetic disks.  Does anybody know of published papers or standards efforts
>> covering filesystem/archive formats for optical disks?
>> 
>
>
>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
>  ... [deleted for brevity]

I have notes of a conversation with (either) Don Wilde or Mike Konshak of
Optotech, Inc. at NCC in July 1985.  One of the two developed an efficient
scheme for bitmap updating on optical media so that files could be updated
efficiently.

Optotech is in Colorado Springs, 303-570-7500.

Rob Lake