Changing maximum block size for a tape

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Changing maximum block size for a tape

Ivan Adzhubey
Hi,

Can a tape written by Bacula with one MaximumBlockSize value be reused after
changing MaximumBlockSize to a different value? I mean, not the data on the
tape, I understand all data will be lost, but can the tape itself be relabeled
and then used with a different block size configured?

The reason I am asking is the following recent post from Kern Sibbald saying
you will not be able to reuse tapes written with a different block size after
you change it:

https://sourceforge.net/p/bacula/mailman/message/35871159/

> > 1. Is it safe (Bacula 7.XX) to set the block size to something other
> > than 64K?
>
> Yes.  However, once you have written a tape with a given block size, you
> cannot changed the block size unless you re-initialized the tape.

What does "re-initialize" means here? I thought you cannot re-initialize a LTO
format tape because of the servo tracks which are hardwritten during
manufacturing.

Thanks,
Ivan

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Ivan Adzhubey, Ph.D.
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Brigham & Women's Hospital
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tel.: (617) 525-4728
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Re: Changing maximum block size for a tape

Kern Sibbald
Yes, the tape can be reused.  Just mount it, rewind it, and write one or
preferably two EOF marks.  Then you will need to relabel for Bacula.

- either stop bacula or release the tape drive

- mt -f /dev/nstxxx rewind

-mt -f /dev/nstxxx weof 2

...



On 06/02/2017 09:59 PM, Ivan Adzhubey wrote:

> Hi,
>
> Can a tape written by Bacula with one MaximumBlockSize value be reused after
> changing MaximumBlockSize to a different value? I mean, not the data on the
> tape, I understand all data will be lost, but can the tape itself be relabeled
> and then used with a different block size configured?
>
> The reason I am asking is the following recent post from Kern Sibbald saying
> you will not be able to reuse tapes written with a different block size after
> you change it:
>
> https://sourceforge.net/p/bacula/mailman/message/35871159/
>
>>> 1. Is it safe (Bacula 7.XX) to set the block size to something other
>>> than 64K?
>> Yes.  However, once you have written a tape with a given block size, you
>> cannot changed the block size unless you re-initialized the tape.
> What does "re-initialize" means here? I thought you cannot re-initialize a LTO
> format tape because of the servo tracks which are hardwritten during
> manufacturing.
>
> Thanks,
> Ivan
>


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Maximum Bacula Block Size

Kern Sibbald
In reply to this post by Ivan Adzhubey
Hello,

Recently on this list we have discussed Maximum Block Size.  In looking
more carefully at the code, I realize that the Maximum Block Size is
currently set at 20,000,000 rather than the 2 or 4 Megabytes that I
probably mentioned (incorrectly).  So, although I do not recommend it,
those of you who would prefer gigantic block sizes, you should be able
to do so without modifying Bacula source code.

Best regards,
Kern

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