Hi all,
2014/1/24 Jeremy Linton <jlinton@xxxxxxxxxxxxx>:
> On 1/23/2014 4:02 PM, Matthias Eble wrote:
>> So: should open() fail on a reserved tape device?
>
> Yes, this is expected behavior for tape devices, reserve 6/release is sometimes
> used by backup applications in SAN environments as an arbitration mechanism
> across multiple machines.
You hit the nail on the head. Problem is that our backup application
does inquiry on /dev/nst*,
which is broken when the same application uses RESERVE/RELEASE.
> Its not that the INQUIRY is failing, its that the st open sequence is doing a
> reserve/TUR/etc during the open.
This is exactly what I am facing. I just thought that it might not be
OK to issue these commands with st_open. But I guess, there is no
right or wrong it's just implemented that way - so applications need
to deal with it and use a generic device.
> If that fails then you can't open the drives sufficiently to send a inquiry via
> pass-through. In some environments you can bypass that processing with
> O_NDELAY/O_NONBLOCK. Or you just use the sg device which doesn't perform the
> tape open processing that st does.
I guess you mean operating systems with environments, as sg_vpd
also uses O_NONBLOCK, which doesn't help:
open("/dev/st15", O_RDONLY|O_NONBLOCK) = -1 EIO (Input/output error)
But as this behaviour has been there for long time, the backup vendor
needs to fix it IMO.
Thanks to all of you
Matthias
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