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Should drive compression be disabled before erasing a tape?

Posted by George Sinclair - NOAA Federal 
George Sinclair - NOAA Federal
Should drive compression be disabled before erasing a tape?
November 27, 2017 05:59PM
Not specifically a NetWorker question.

If erasing LTO tapes using `mt -f device erase` (long erase, so at least
2 hours), should compression first be turned off for the tape device?

Does it matter?

Thanks.

George

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George Sinclair
Voice: (301) 713-4921
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- Any opinions expressed in this message are NOT those of the US Govt. -


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On tisdag 28 november 2017 kl. 03:47:33 EET you wrote:
> Not specifically a NetWorker question.
>
> If erasing LTO tapes using `mt -f device erase` (long erase, so at least
> 2 hours), should compression first be turned off for the tape device?
>
> Does it matter?

Doesn't matter.

Best
Dag


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George Sinclair - NOAA Federal
Re: Should drive compression be disabled before erasing a tape?
November 30, 2017 12:59PM
On 2017-11-28 00:23, Dag Nygren wrote:
> On tisdag 28 november 2017 kl. 03:47:33 EET you wrote:
>> Not specifically a NetWorker question.
>>
>> If erasing LTO tapes using `mt -f device erase` (long erase, so at least
>> 2 hours), should compression first be turned off for the tape device?
>>
>> Does it matter?
> Doesn't matter.
Thanks. I was hunting around here and elsewhere, and I couldn't find
anything on this. Maybe it's a matter of the proper strings, or nobody
asks. Anyway, I was thinking that if one was using /dev/zero, say, with
dd, and erasing in that matter, then maybe it would make sense -- not
saying, but maybe -- to turn off compression given that that would
ideally compress and thus take longer? I've erased like that before, but
I don't recall if I first turned compression off. Anyway, as I recall,
the total time was not vastly different from 'mt erase', but again, I
don't remember what the compression settings were in those tests or if I
even compared times with the compression setting on versus off. I don't
know how 'mt erase' works compared with the dd example, and if their
differences (if any) matter, thus the question.

> Best
> Dag
>
>


--
George Sinclair
Voice: (301) 713-4921
- The preceding message is personal and does not reflect any official or unofficial position of the United States Department of Commerce -
- Any opinions expressed in this message are NOT those of the US Govt. -


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This list is hosted as a public service at Temple University by Stan Horwitz
If you wish to sign off this list or adjust your subscription settings, please do so via http://listserv.temple.edu/archives/emc-dataprotection-l.html
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On torsdag 30 november 2017 kl. 22:05:07 EET you wrote:
> On 2017-11-28 00:23, Dag Nygren wrote:

> > Doesn't matter.
>
> Thanks. I was hunting around here and elsewhere, and I couldn't find
> anything on this. Maybe it's a matter of the proper strings, or nobody
> asks. Anyway, I was thinking that if one was using /dev/zero, say, with
> dd, and erasing in that matter, then maybe it would make sense -- not
> saying, but maybe -- to turn off compression given that that would
> ideally compress and thus take longer? I've erased like that before, but
> I don't recall if I first turned compression off. Anyway, as I recall,
> the total time was not vastly different from 'mt erase', but again, I
> don't remember what the compression settings were in those tests or if I
> even compared times with the compression setting on versus off. I don't
> know how 'mt erase' works compared with the dd example, and if their
> differences (if any) matter, thus the question.

The difference here is that dd writes blocks with zeroes onto
the tape in blocks, but still in the format requested.

mt erase sends a low level erase instruction to the
tape drive which will then "remove" the blocks
alltogether.

Best lock
Dag


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