Re: Xen FreeBSD domU block I/O problem on -current only affects reads > 1024 bytes

At Tue, 20 Apr 2021 16:53:58 -0700, "Greg A. Woods" <[email protected]> wrote:
Subject: Re: Xen FreeBSD domU block I/O problem on -current only affects reads > 1024 bytes
>
> With the gracious help of RVP <[email protected]> I have been able to identify
> better what is actually going wrong with FreeBSD's access to NetBSD dom0
> xbdback(4) storage.
>
> It seems that in certain circumstances (e.g. in newfs and the test
> program) whenever FreeBSD issues a read of more than 1024 bytes only the
> first 1024 bytes are correct -- the rest of the bytes returned come from
> somewhere else on the disk, which appears to be starting at six(6)
> sectors after where they were supposed to have come from.  Note that
> this corresponds to exactly 4096 bytes offset from the beginning of the
> read.

Reviving this old thread with some new info....

It seems ZFS either doesn't issue large read requests, and/or it works
around the problem in some other way.

With the help of a custom FreeBSD kernel with ZFS compiled in, and
booting it as a PVH domU kernel, and with the new(ish) FreeBSD (14.0)
way of installing with a ZFS root, I have a couple of domUs running just
fine now, one even recovered old zpools on the machine where I first
experienced this problem!

As soon as possible, especially if I can dredge up another test server,
I'll test plain UFS again with a NetBSD 10.0_RC2 kernel as dom0.

--
					Greg A. Woods <[email protected]>

Kelowna, BC     +1 250 762-7675           RoboHack <[email protected]>
Planix, Inc. <[email protected]>     Avoncote Farms <[email protected]>

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