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From: danderson@allvax.enet.dec.com (Dave Anderson)
Newsgroups: comp.periphs.scsi
Subject: Re: DATs writes unspacable erase zone?
Message-ID: <3290@ryn.esg.dec.com>
Date: 24 Oct 90 15:56:49 GMT
Sender: guest@ryn.esg.dec.com
Organization: Digital Equipment Corporation
Lines: 32


In article <9850001@hpcpbla.HP.COM>, kev@hpcpbla.HP.COM (Kevin Jones) writes...
>Assuming the DAT Drive writes DDS format tapes (HP, SONY, Archive,
>WangTEC, WangDAT ...)
> 
>You are correct in assuming the drive puts down an erase zone at
>end of data.
> 
>In fact, it writes a specific "End Of Data" pattern which it can
>detect on subsequent passes (even at x200 speed).
> 
>...
> 
>The DDS format specifies that anything on tape FOLLOWING an end of
>data pattern, within the current partition, is UNDEFINED.
> 
>In short, DDS does not allow "tricks" involving the recovery of
>beyond EOD data. ...

So DAT/DDS was deliberately designed to make it totally impossible to ever read
any data beyond EOD?  Is one supposed to cheerfully write off the gigabyte of
vital data that's still on a backup tape that someone accidentally wrote over
the beginning of?  While I understand (and agree with) the premise that
'rewrite in place' is unreliable and should not be attempted, there are
certainly cases where the ability to read whatever data remains on a partially
written-over tape can be vitally important! 

It sounds like a very bad idea to use this format for backups.

	Dave

[The above is my opinion only -- I don't know of anyone else who'd want it.]