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Re: Question about instance volumes


As Ivan explained, when there is brand new template used, ACS will copy it
from Secondary Storage to Primary Storage, this image will become "parent"
/ backing / gold image, and is locked as Read Only. Any new VM will have
it's volume "linked" as child image to this parent image.
This is done to

1) Save space (imagine 100GB template), and you deploy 100 VMs = maybe
101GB totally used really...(until you write some new data - it is written
to child images) vs 10000GB if it would be separate images.

2) This also brings some performance benefits, since you read from 1 x
100GB image, not from 100x 100GB images...

Cheers


On 23 April 2018 at 03:59, Ivan Kudryavtsev <kudryavtsev_ia@xxxxxxxxx>
wrote:

> Hi.
>
> When you create a VM from a template then ACS doesn't copy the template to
> a new root image, but creates it thin, pointing the volume to the template
> as a backing store device.
>
> пн, 23 апр. 2018 г., 8:16 Felipe Arturo Polanco <felipeapolanco@xxxxxxxxx
> >:
>
> > Hello,
> >
> > I am seeing a behavior that I would like to ask about.
> >
> > I have some instances that instead of having a normal qcow2 disk file,
> have
> > a qcow2 file that points to another backing store file.
> >
> > eg:
> >
> > <disk type='file' device='disk'>
> >       <driver name='qemu' type='qcow2' cache='none'/>
> >       <source file='/mnt/ps4/c6a79f0b-60b2-419c-98af-6ae854f88ad1'/>
> >       <backingStore type='file' index='1'>
> >         <format type='raw'/>
> >         <source file='/mnt/ps4/ddc78c68-47b2-43ef-9109-4c91ebb8bda5'/>
> >         <backingStore/>
> >       </backingStore>
> >       <target dev='vda' bus='virtio'/>
> >       <serial>c6a79f0b60b2419c98af</serial>
> >       <alias name='virtio-disk0'/>
> >       <address type='pci' domain='0x0000' bus='0x00' slot='0x04'
> > function='0x0'/>
> >     </disk>
> >
> > I am reading online that this is seen when there is a snapshot of another
> > disk file, but I have no snapshots, just a regular Linux server that I
> > created through the Cloudstack UI.
> >
> > Any idea of why this would happen? Not all Instances have this backing
> > storage file.
> >
> > Thanks,
> >
>



-- 

Andrija Panić