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[Marco CONSONNI <mcocmo62@xxxxxxxxx>]

Hi Ahmed,

very technical questions.
I'm not sure my answers are right: I'm just an user...

In order to answer, I've just look at what happens and made some guess.
Feel free to verify yourself.

I'm assuming you are using KVM as I'm doing.

The space for the boot disk and the ephemeral disk should be represented as
files in the physical node where the VM is hosted.
In order to check that, go to directory  /var/lib/nova on the node where
the VM is running.
As far as I understand, this is where nova (and KVM) keep the running
instances' information.
You should see a directory for each running instance named as
instance-xxxxxxx, where xxxxxxx uniquely identifies an instance (there are
several ways for uniquely identify an instance, this is one of many... but
this is a different story).
Go into one of these and check what you find.

For what concerns nova-scheduler, I don't know what exactly does. I'm
afraid that you need to test and see what happens.

A nova command can help for inspecting what a node is using, in terms of
resources.

At the controller node (or any other node where you installed nova client),
type the following command substituting OpenStack02 with the name of the
node you want to inspect:

*$ nova host-describe OpenStack02*

+-------------+----------------------------------+-----+-----------+---------+

| HOST        | PROJECT                          | cpu | memory_mb |
disk_gb |

+-------------+----------------------------------+-----+-----------+---------+

| OpenStack02 | (total)                          | 16  | 24101     | 90
|

| OpenStack02 | (used_max)                       | 13  | 7680      | 0
|

| OpenStack02 | (used_now)                       | 13  | 8192      | 0
|

| OpenStack02 | 456ec9d355ae4feebe48a2e79e703225 | 4   | 2048      | 0
|

| OpenStack02 | fb434e07b687494bb669fde23f497970 | 9   | 5632      | 0
|

+-------------+----------------------------------+-----+-----------+---------+

It return a brief report of the resources currently used by a node.

To my knowledge,  the dashboard does not provide a similar page, at the
time being.

Hope it helps,
Marco.



On Tue, Dec 4, 2012 at 4:40 PM, Ahmed Al-Mehdi <ahmedalmehdi@xxxxxxxxx>wrote:

> Hi Marco,
>
> Thank you very much for the info, much much clearer.  I was looking for
> the boot disk using "ls -l /dev/sd*", but the existence of /dev/vda1
> should have given me a clue.
>
> A few follow up questions:
>
> - I am assuming the space for the VM boot disk is allocated from the
> local hard disk of the physical host on which the VM is instantiated,
> right?
> - If Yes
>    - How is the boot disk represented on the physical host.  Is it a file
> on the local filesystem that represent the VM boot disk?
>    - I am guessing there is some logic in nova-scheduler that checs
> first if there is enough disk apace on the physical host for the VM(along with RAM,
> VCPUs) before launching the VM on the host?
>    - Is there any way to find out from Horizon how much disk space is
> available on a (or each) physical host for VM boot disk allocation?
>
> Thank you,
> Ahmed.
>
>
>
>
> On Tue, Dec 4, 2012 at 12:07 AM, Marco CONSONNI <mcocmo62@xxxxxxxxx>wrote:
>
>> Hello,
>>
>>
>> When you use a flavor with an ephemeral disk size different from zero,
>> the instance is booted with an extra virtual disk whose size is indicated
>> by the ephemeral value (in GB).
>>
>> Using cirros image, try a flavor with ephemeral disk size different from
>> zero (you need to create one yourself because the "standard" flavors have
>> ephemeral size equal to 0), then log into the just booted instance and type:
>>
>>
>> *$ ls /dev/vd**
>>
>> /dev/vda   /dev/vda1  /dev/vdb
>>
>>
>>
>> Disk /dev/vdb is a (virtual) disk, automatically created at boot time,
>> corresponding to the ephemeral disk space indicated by the flavor . Please
>> note that /dev/vda, mounted as /dev/vda1, is the boot disk, always created
>> when you boot an instance.
>>
>> Verify the size of the available disks; more specifically, verify
>> /dev/vdb:
>>
>> *
>> *
>>
>> *$ sudo fdisk -l*
>>
>> Disk /dev/vda: 1073 MB, 1073741824 bytes
>>
>> 255 heads, 63 sectors/track, 130 cylinders, total 2097152 sectors
>>
>> Units = sectors of 1 * 512 = 512 bytes
>>
>> Sector size (logical/physical): 512 bytes / 512 bytes
>>
>> I/O size (minimum/optimal): 512 bytes / 512 bytes
>>
>> Disk identifier: 0x00000000
>>
>>
>>
>>    Device Boot      Start         End      Blocks   Id  System
>>
>> /dev/vda1   *       16065     2088449     1036192+  83  Linux
>>
>>
>>
>> Disk /dev/vdb: 1073 MB, 1073741824 bytes
>>
>> 16 heads, 63 sectors/track, 2080 cylinders, total 2097152 sectors
>>
>> Units = sectors of 1 * 512 = 512 bytes
>>
>> Sector size (logical/physical): 512 bytes / 512 bytes
>>
>> I/O size (minimum/optimal): 512 bytes / 512 bytes
>>
>> Disk identifier: 0x00000000
>>
>>
>>
>> Disk /dev/vdb doesn't contain a valid partition table
>>
>>
>>
>> Please note that /dev/vdb is made available as raw device, meaning that
>> you need to partition and format it before using.
>>
>> You can find instructions on how to do that here
>> http://docs.openstack.org/folsom/openstack-compute/admin/content/configure-nova-volume.html(search for command fdisk)
>>
>> Also note that this disk, being ephemeral, disappears when you terminate
>> the VM. If you want to keep the data you produce with a VM that is destined
>> to be terminated, you need to use Volumes that you explicitly create and
>> attach using the services implemented by Cinder (former nova-volume).
>>
>>
>> For what concerns the size you define for the boot disk, try and lunch
>> two instances: one with flavor m1.tiny the other with m1.small:
>>
>>
>> -- tiny --
>>
>> *$ sudo fdisk -l
>> *
>> Disk /dev/vda: 41 MB, 41126400 bytes
>> 255 heads, 63 sectors/track, 5 cylinders, total 80325 sectors
>> Units = sectors of 1 * 512 = 512 bytes
>> Sector size (logical/physical): 512 bytes / 512 bytes
>> I/O size (minimum/optimal): 512 bytes / 512 bytes
>> Disk identifier: 0x00000000
>>
>>    Device Boot      Start         End      Blocks   Id  System
>> /dev/vda1   *       16065       80324       32130   83  Linux
>>
>>
>> -- small --
>>
>>
>> *$ sudo fdisk -l
>> *
>> Disk /dev/vda: 21.5 GB, 21474836480 bytes
>> 255 heads, 63 sectors/track, 2610 cylinders, total 41943040 sectors
>> Units = sectors of 1 * 512 = 512 bytes
>> Sector size (logical/physical): 512 bytes / 512 bytes
>> I/O size (minimum/optimal): 512 bytes / 512 bytes
>> Disk identifier: 0x00000000
>>
>>    Device Boot      Start         End      Blocks   Id  System
>> /dev/vda1   *       16065    41929649    20956792+  83  Linux
>>
>>
>> As you notice, the size indicated by the flavor has effects on the size
>> of the boot disk.
>>
>>
>> Hope it helps,
>> Marco.
>>
>>
>>
>>
>> On Mon, Dec 3, 2012 at 7:03 PM, Ahmed Al-Mehdi <ahmedalmehdi@xxxxxxxxx>wrote:
>>
>>> Hello,
>>>
>>> I instantiated a VM using the cirros image, using the pre-defined
>>> "m1.small" (1 VCPU, 2 GB Ram, 20G boot disk, 0 Ephemeral disk).  I then
>>> logged into the console of the VM to view some system stats.  The num of
>>> CPU and memory makes sense, but I am a bit confused on the storage aspect.
>>>  I see the output of "df -h " as following:
>>>
>>> $ df -h
>>> Filesystem              Size         Used            Available      Use%
>>>     Mounted on
>>> /dev                  1001.1M              0              1001.1M
>>>   0%         /dev
>>> /dev/vda1             23.2M        12.9M                   9.1M
>>> 59%         /
>>> tmpfs                1004.1M              0              1004.1M
>>> 0%         /dev/shm
>>> tmpfs                  200.0K        20.0K                180.0K
>>> 10%         /run
>>>
>>>
>>> What is the difference between Boot disk and Ephemeral disk?
>>>
>>> How can I correlate the 20G boot disk to the output of "df -h".
>>>
>>>
>>> Regards,
>>> Ahmed.
>>>
>>>
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>>
>