[Bug 226583] FreeBSD VM on Hyper-V/Azure can't properly detected SCSI disk da2

[bugzilla-noreply at freebsd.org]

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=226583

--- Comment #1 from Dexuan Cui <decui at microsoft.com> ---
When the issue happens, the Azure host (in the VM, "dmesg |grep  "Hyper-V
Version" shows: "Hyper-V Version: 10.0.14393 [SP0]) reports da2 as a SPC-2
device. I tried to reproduce the bug on local Hyper-V hosts (which always
report da2 as a SPC-3 device), but I couldn't repro it.

So far, I can only reproduce the bug with some specific VM sizes, e.g. Standard
D4 v2 (8 vcpus, 28 GB memory) ) in West Central US region. Note: some people
also reported some other VM sizes can also reproduce the bug. It looks all the
affected VM sizes use HDD-backed disks. If we create a VM with SSD-backed
disks, the bug can't repro. And, with a HDD-backed disk, if we avoid attaching
the disk to LUN0, it looks the bug can't repro either.

So, two possible mitigation solutions are: a) use a VM size that supports
SSD-backed disks; b) attach any extra data disk to a LUN whose number is not
zero.

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