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RE: [Xen-devel] [Patch 0/7] pvSCSI driver

To: "Jun Kamada" <kama@xxxxxxxxxxxxxx>
Subject: RE: [Xen-devel] [Patch 0/7] pvSCSI driver
From: "James Harper" <james.harper@xxxxxxxxxxxxxxxx>
Date: Thu, 21 Feb 2008 16:30:09 +1100
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Thread-topic: [Xen-devel] [Patch 0/7] pvSCSI driver
> Hi James-san,
> On Thu, 21 Feb 2008 14:39:47 +1100
> "James Harper" <james.harper@xxxxxxxxxxxxxxxx> wrote:
> > Just responding to myself, would I be guessing correctly that you
> > removed the timeout field to make the request structure smaller? The
> That is one reason. However, the main reason is as follows.
> The time that guests/host will get is not real world's time on
> virtualized environment. The time depends on hypervisor's scheduling.
> (Is this assumption right ?)
> For example, if upper layer of the pvSCSI frontend specified 5 seconds
> as timeout, it should be treated as real world's time or within a
> domain's world time ?
> We didn't have clear answer when we implemented that part. Therefore,
> we coded it temporally 5 seconds.
> James-san, how do you think about this issue ?

I don't think the exact value of the timeout matters that much. At
worst, a 5 second timeout is going to be at least 5 seconds, and
probably not much more than that. It's the Linux SCSI subsystem itself
that handles the timeout anyway.

> By the way, we understand that the 5 seconds is too short to support
> tape device.

Yes, way too short. For running the HP LT&T (Library and Tape Tools),
even 60 seconds is too short for some operations.

FYI, I have the HP LT&T working nicely under windows now. All tests
succeed, even a firmware update to the tape drive worked. A Read/Write
test on a HP LTO2 drive with LTO1 media gives me 13.3MB/s (approx
800MB/minute) for both read and write operations. I assume that a CD or
DVD burner would work also, although I don't have one to test.

Are you planning on requesting that pvSCSI get merged into the Xen tree
once you have the timeout and unload issues sorted out?


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