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RE: [Xen-devel] vscsi and /dev/tape/by-path

To: "Konrad Rzeszutek Wilk" <konrad.wilk@xxxxxxxxxx>
Subject: RE: [Xen-devel] vscsi and /dev/tape/by-path
From: "James Harper" <james.harper@xxxxxxxxxxxxxxxx>
Date: Wed, 12 Jan 2011 08:00:47 +1100
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Thread-topic: [Xen-devel] vscsi and /dev/tape/by-path
> On Tue, Jan 11, 2011 at 01:41:29PM +1100, James Harper wrote:
> > I use vscsi fairly extensively (under Windows mainly for testing
> > baremetal restores from tape), and have a problem that's been
bugging me
> > for ages. If I use "/dev/st4" it works fine, but obviously that's
> > hopeless unreliable as it relies on device enumeration order at
boot. I
> > want to use something like "
> > /dev/tape/by-path/pci-0000:01:08.0-scsi-0:0:3:0-st" so that I am
> > guaranteed of getting the right drive, but vscsi doesn't appear to
> > support it.
> >
> > Digging into it, I see function vscsi_get_hctl_and_devname_by that
> > attempts to figure out the sg device that corresponds to whatever I
> > specified in the config file. If I could modify that function to
> > follow the symlinks until I get to a real device that would probably
> > sufficient, but is that the right way to do it?
> Yup. Thought I would think that using the /dev/by-uuid/ would be a
> way of doing it in case you want to passthrough a SCSI disk for

For disk, /dev/disk/by-uuid might be a better option, although it
depends on your requirements. For tape, my system /dev/tape/by-path is
the only available option on my system, although I could probably create
a /dev/tape/by-id path easily enough using the serial number or
something. by-id would allow the device to be moved across different
busses and still remain the same, but obviously breaks when a tape drive
fails and has to be replaced, which happens fairly regularly.

This is the advantage of having so many choices :)

> Thought what if you want to pass in a SCSI scanner? Would that work?

Do they still exist? :)


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