Hi,
06.11.2007 22:39,, John Huttley wrote::
> Hi folks,
> I'm trying to get my head around the details of tape devices, as in
> /dev/st0.
> I had thought that for each physical device, two nodes were created
> /dev/st0 and /dev/nst0.
> The latter does not rewind when closed, thats the one used with bacula.
>
> Untrue! its creates 8 modes. For each on st and nst, there are {a,l,m}
> suffixes. These are "scsi modes".
Yup.
> Its documented that these have their own minor device numbers, but I
> haven't found anything that explains the significance.
I admit /usr/src/linux/Documentation/st.txt is hard to understand and
isn't very explicit... the key point, I think, is the following paragraph:
Many Unices contain internal tables that associate different modes to
supported devices. The Linux SCSI tape driver does not contain such
tables (and will not do that in future). Instead of that, a utility
program can be made that fetches the inquiry data sent by the device,
scans its database, and sets up the modes using the ioctls. Another
alternative is to make a small script that uses mt to set the defaults
tailored to the system.
In other words, there are no standard modes defined. It's up to your
distribution, or your system administrator, what they set.
I never used the different pre-set modes; whenever I needed to change
the driver's behaviour, I used mt and its options like stoptions and
stwrthreshold.
> I even had a grovel through st.c but didn't get anything but a pain
> behind my eyes.
The reference to this pain is in Documentation/st.txt :-)
> Any comment on these would be most welcome.
Ignore the extra modes :-)
Arno
> Regards,
> John
>
>
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--
Arno Lehmann
IT-Service Lehmann
www.its-lehmann.de
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