Re: drive compression discovery
2003-03-10 22:11:43
On Mon March 10 2003 14:13, Eric Sproul wrote:
>Hi all,
>I'm familiar with the general theory of how to "rescue" an AMANDA
> tape that's been written with drive compression turned on.
> Here's my situation:
>
>I've completed my first dumpcycle with my current config, and I'm
>fairly certain that drive compression has been turned off the
> whole time, but I'm not 100% sure. I now have in place a script
> that ensures drive compression is off, but it was not put in
> place until a number of runs had been done. I want to make sure
> all the tapes are uncompressed before I reuse them.
>
>My question: If I do a dd of some amount of data (like dumping
> the first 32K of data as I would if I was saving the label), and
> then see (via mt) that the drive's compression is still off, is
> it safe to conclude that the tape was written with compression
> off?
>
I believe so. If the drive has a front panel indicator of
compression use like mine does, I'd use that for the last word.
>I've read posts that indicate a compressed tape will silently set
> drive compression back on, but will that change still be visible
> to mt?
AFAIK, yes.
>BTW, the drive has no DIP switches for setting compression--
That would definitely be unusual... The lawyers have attacked the
user stuff in the packaging to the point where it may not be
mentioned (I mean "Now why would the *user* need to know that?),
and I'd come a lot closer to being able to believe that as opposed
to its not having any jumpers or dip switches at all to control its
powerup defaults.
> it is
>completely controlled by software. Also, my system is Linux, so
> there are no compression-related device names. I am relying
> strictly on mt to manipulate the drive outside of AMANDA, so it's
> important that I be able to trust its output.
How are you interpreting the mt report so as to define if
compression is on or off? I don't recall seeing that in plain
english in any mt output report since about RH5.2, and it has
changed a bit. Its concise to the point of being obtuse IMO.
--
Cheers, Gene
AMD K6-III@500mhz 320M
Athlon1600XP@1400mhz 512M
99.24% setiathome rank, not too shabby for a WV hillbilly
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