FreeBSD 10 on Hyper-V


Good news: _Both_ FastIDE and CD-Rom work in FreeBSD 10 on Hyper-V

Good news:
_Both_ FastIDE and CD-Rom work in FreeBSD 10 on Hyper-V…revision=256304
Revision 256304
Modified Thu Oct 10 22:46:49 2013 UTC
. . .
Allow the legacy CDROM device to be accessed in a FreeBSD guest,
while still using enlightened drivers for other block devices.
. . .

Details, and some info for Hyper-V sysadmins :

Microsoft hyperv dev team:

One of the issues with Hyper-V is that it does not virtualize the CD device and therefore
we rely on the ATA driver in the guest operating system to manage CDROMs.
What we would like to do is disable the ATA driver for all device types except the CDROM in the presence of Hyper-V.

vvm :

>> Disable both primary and secondary ATA controller prevent use CD-ROM
>> device in VM ( guest)
>> Because "synthetic storage driver" not handle CD-ROM devices
>> ( IMHO, even more: Hyper-V host work with CD-ROM only as "PCI bus" device)

mav@ :

A.M.> Then may be possibility of blocking/hiding specific ATA channels or
A.M.> devices could be investigated.

mav@ :
>> Unfortunately, CAM subsystem used for both ATA and SCSI stacks in
>> FreeBSD 9.x and above is mostly unaware of "NewBus" infrastructure
>> used for driver probe and attachment. That is why you can’t replace
>> driver for a single disk in the same way as you replaced driver for
>> the whole controller. The highest level present in "NewBus" is ATA
>> channel. So if disk and CD-ROM are always live on different channels,
>> you can create dummy driver not for the whole controller (atapciX),
>> but for single hardcoded ATA channel (ataX).

Microsoft hyperv dev team:

> We have decided to have the DVD and the root device on different channels
> as that appears to be the simplest way to address this problem.
. . .
> . . . dummy driver for a single hardcoded ATA channel.
>The boot device has to be on the first channel,
> this would require the ISO device to be on the second channel.

mav@ :
Revision 256304 (view) . . .- [select for diffs]
Modified Thu Oct 10 22:46:49 2013 UTC
File length: 5783 byte(s)

Allow the legacy CDROM device to be accessed in a FreeBSD guest, while
still using enlightened drivers for other block devices.

Submitted by:	Microsoft hyperv dev team, mav@
Approved by:	re@


From: vvm
To: mav@
Thanks for patch!

Microsoft hyperv dev team:
Thanks Alexander.

Microsoft hyperv dev team:
We tested the patch and it seems to work fine.
We observed that the CDROM is not accessible on channel 0 but is accessible on channel 1 as intended.
The solution is good enough as the Hyper-V UI in general biases a user
to attach the root device to channel 0
and the CDROM to channel 1
and we can further reinforce this for FreeBSD users.
I think this solution is good enough for now and we can explore more later.

Yes: "this solution" (
"the root device to channel 0" with syntectic ATA driver ,
"CDROM accessible on channel 1" with non-Hyper-V specific ATA driver
) "is good enough for now"

1) "this solution" "will let the ATA driver install FreeBSD"
2) and is "way to enable FastIDE"


Microsoft hyperv dev team:
Many many thanks for getting this to work.


ToDo: check this with



FreeBSD in Hyper-V R2

Convert to .VHD FreeBSD-10.0-ALPHA4-amd64-memstick.img

Attach as disk to secondary ATA channel, boot and install:

— syntetic LANCard work ( may be need run "dhclient hn0" )



Sorry for short post: I’m not shue, what can public some private e-mail messages,
best ask about details in comment or by e-mail

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