Xen users - Oct 2012 - How can I uniquely identify my disk in guest OS on Xenserver?

Hi all,

I have installed RHEL6 as guest OS on Citrix Xen Server. After installation
of OS, I can see disk names as /dev/xvda, /dev/xvdb instead of traditional
convention like /dev/sda, /dev/sdb on guest OS.

Generally, on physical machines, in /proc/scsi/scsi file, we get a unique
entry for every disk connected to the system. For e.g. string
"scsi02:00:00:01"
indicates that this disk is connected to the machine via Host=2, Channel=00,
Id=00 Lun=01. This helps me in my project to uniquely identify each and
every disk in scenarios where many times after reboot OR in SAN boot cases
OR in some Disaster Recovery procedures, disk names might change from say
/dev/sda to /dev/sdb after reboot. But, this Host:Channel:ID:Lun combination
remains same for every disk and I can uniquely identify the disks though
their /dev/sd* names have changed.

For my project, on Citrix Xenserver, I need to know the unique disk
location for such Xen guest OS devices by which I can easily identify disks
across the reboots for the above mentioned cases.

So, I have couple of questions on this front. Please help me out or guide
me for the same.

1. As /proc/scsi/scsi don''t have such entry for /dev/xvdX type disks,
do we
have similar mechanism in Citrix XenServer to identify our guest OS disks
uniquely?

2. This question is rather a continuation of previous one. While searching
answer for above question, I found that for every /dev/xvdX disk, a unique
device entry is present in /sys/block/xvdX/ directory in the format
"vbd-XXX", for example, vbd-768, vbd-832, etc.
Here, vbd stands for Virtual Block Device.
But what is the significant of the numbers 768, 832 ,etc.? How these are
generated? Are they indicatingsomething like Host:Channel:Id:Lun? Can I
trust these numbers to distinctly identify my disks? Are these numbers
differ from one guest OS to other OR depend on Xenserver configuration?


Please suggest me some answer on this front.

Thanks in advance.

Regards,
Neo


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2012/10/15 neo3 matrix <neo3matrix@gmail.com>:
> Hi all,
>
> I have installed RHEL6 as guest OS on Citrix Xen Server. After installation
> of OS, I can see disk names as /dev/xvda, /dev/xvdb instead of traditional
> convention like /dev/sda, /dev/sdb on guest OS.
>
> Generally, on physical machines, in /proc/scsi/scsi file, we get a unique
> entry for every disk connected to the system. For e.g. string
> "scsi02:00:00:01" indicates that this disk is connected to the
machine via
> Host=2, Channel=00, Id=00 Lun=01. This helps me in my project to uniquely
> identify each and every disk in scenarios where many times after reboot OR
> in SAN boot cases OR in some Disaster Recovery procedures, disk names might
> change from say /dev/sda to /dev/sdb after reboot. But, this
> Host:Channel:ID:Lun combination remains same for every disk and I can
> uniquely identify the disks though their /dev/sd* names have changed.
>
> For my project, on Citrix Xenserver, I need to know the unique disk
location
> for such Xen guest OS devices by which I can easily identify disks across
> the reboots for the above mentioned cases.
>
> So, I have couple of questions on this front. Please help me out or guide
me
> for the same.
>
> 1. As /proc/scsi/scsi don''t have such entry for /dev/xvdX type
disks, do we
> have similar mechanism in Citrix XenServer to identify our guest OS disks
> uniquely?
>
> 2. This question is rather a continuation of previous one. While searching
> answer for above question, I found that for every /dev/xvdX disk, a unique
> device entry is present in /sys/block/xvdX/ directory in the format
> "vbd-XXX", for example, vbd-768, vbd-832, etc.
> Here, vbd stands for Virtual Block Device.
> But what is the significant of the numbers 768, 832 ,etc.? How these are
> generated? Are they indicatingsomething like Host:Channel:Id:Lun? Can I
> trust these numbers to distinctly identify my disks? Are these numbers
> differ from one guest OS to other OR depend on Xenserver configuration?


Hello,
Disk are visible as xvda, because these using paravirtualization

For thou because the question appear in /proc/scsi/ s as are scsi
disks (are virtual disks)

Los numbers "VBD-768" is it id it virtual disk.

with the commands from dom0, you can see the relationship id and disk:

XM block-list DomU
xenstore-ls /local/domain/0/backend/tap/4/51728



If the understands are because the use translate.google JA :)

On Mon, 2012-10-15 at 08:02 +0100, neo3 matrix wrote:
> For my project, on Citrix Xenserver,
This list is for users of the Xen.org version of Xen and the associated
toolstack etc. Questions regarding XenServer are better addressed to
your support representative or to the XenServer forums:
http://forums.citrix.com/category.jspa?categoryID=101

Ian.