[Openstack] Understanding "flavors" of VM
Ahmed Al-Mehdi
ahmedalmehdi at gmail.com
Tue Dec 4 17:35:40 UTC 2012
Hi Marco,
This is really good stuff, thank you very much for helping out. I am
creating some instances to test out how/where the different storage related
elements are created.
I created two VM instance:
Instance 1 : 20GB boot disk
Instance 2 : 10GB boot disk, 2 GB Ephemeral disk.
root at bodega:/var/lib/nova# ls -lh -R instances
instances:
total 12K
drwxrwxr-x 2 nova nova 4.0K Dec 4 09:01 _base
drwxrwxr-x 2 nova nova 4.0K Nov 28 11:44 instance-00000001
drwxrwxr-x 2 nova nova 4.0K Dec 4 09:01 instance-00000002
instances/_base:
total 240M
-rw-r--r-- 1 nova nova 40M Dec 4 08:51
8af61c9e86557f7244c6e5a2c45e1177c336bd1f
-rw-r--r-- 1 libvirt-qemu kvm 10G Dec 4 09:01
8af61c9e86557f7244c6e5a2c45e1177c336bd1f_10
-rw-r--r-- 1 nova kvm 20G Dec 4 08:51
8af61c9e86557f7244c6e5a2c45e1177c336bd1f_20
-rw-rw-r-- 1 nova nova 9.4M Nov 28 11:44
8af61c9e86557f7244c6e5a2c45e1177c336bd1f.part
-rw-r--r-- 1 nova nova 2.0G Dec 4 09:01 ephemeral_0_2_None
<======
-rw-r--r-- 1 libvirt-qemu kvm 2.0G Dec 4 09:01 ephemeral_0_2_None_2
<=====
instances/instance-00000001:
total 1.9M
-rw-rw---- 1 nova kvm 26K Nov 28 11:45 console.log
-rw-r--r-- 1 libvirt-qemu kvm 1.9M Dec 4 07:01 disk
-rw-rw-r-- 1 nova nova 1.4K Nov 28 11:44 libvirt.xml
instances/instance-00000002:
total 1.8M
-rw-rw---- 1 libvirt-qemu kvm 27K Dec 4 09:02 console.log
-rw-r--r-- 1 libvirt-qemu kvm 1.6M Dec 4 09:03 disk
-rw-r--r-- 1 libvirt-qemu kvm 193K Dec 4 09:01 disk.local
-rw-rw-r-- 1 nova nova 1.6K Dec 4 09:01 libvirt.xml
root at bodega:/var/lib/nova#
It seems all the boot disk and ephemeral disk are created as files in
/var/lib/nova/instance/_base. I don't understand why there are two files
of size 2GB (lines marked above with <=====). I will look into that later
on.
I am running into an issue creating a volume for which I will post a
separate message.
Thank you again very much.
Regards,
Ahmed.
On Tue, Dec 4, 2012 at 8:56 AM, Marco CONSONNI <mcocmo62 at gmail.com> wrote:
> Sorry, the directory you need to check is /var/lib/nova/instances.
>
> MCo.
>
>
> On Tue, Dec 4, 2012 at 5:54 PM, Marco CONSONNI <mcocmo62 at gmail.com> wrote:
>
>> 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 at gmail.com>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 at gmail.com>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 at gmail.com>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.
>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> Mailing list: https://launchpad.net/~openstack
>>>>> Post to : openstack at lists.launchpad.net
>>>>> Unsubscribe : https://launchpad.net/~openstack
>>>>> More help : https://help.launchpad.net/ListHelp
>>>>>
>>>>>
>>>>
>>>
>>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.openstack.org/pipermail/openstack/attachments/20121204/7ce578cb/attachment.html>
More information about the Openstack
mailing list