[Engine-devel] Floating Disk feature description

[Yaniv Kaul]

On 02/02/2012 01:35 PM, Daniel Erez wrote:
>
> ----- Original Message -----
>> From: "Yaniv Kaul"<ykaul at redhat.com>
>> To: "Daniel Erez"<derez at redhat.com>
>> Cc: engine-devel at ovirt.org
>> Sent: Thursday, February 2, 2012 10:27:06 AM
>> Subject: Re: [Engine-devel] Floating Disk feature description
>>
>> On 02/01/2012 07:04 PM, Daniel Erez wrote:
>>> Hi,
>>>
>>> Floating Disk feature description Wiki page:
>>> http://www.ovirt.org/wiki/Features/DetailedFloatingDisk
>>>
>>> Best Regards,
>>> Daniel
>>> _______________________________________________
>>> Engine-devel mailing list
>>> Engine-devel at ovirt.org
>>> http://lists.ovirt.org/mailman/listinfo/engine-devel
>> 0. Is it a floating disk or a floating image? would be nice to use
>> the
>> same terminology for all projects, where possible
>> (http://www.ovirt.org/wiki/Vdsm_Storage_Terminology#Image)
> Disk and Image are the same ("Disk" is the RHEV-M term for VDSM's "Image"). Both of them means: the collection of "volumes" (or, "DiskImages", in RHEV-M terminology) that comprise the full disk. We have no problem using either terminology, however might be confusing either way.
> [BTW, a floating disk can't conatin snapshots - so it doesn't really matter if you are talking about disk, image, diskImage or volume - they are all the same]

If they are the same, then please use the term 'image'.
And it looks like the feature is 'floating single-volume image' . I 
wonder if the limitation is really an issue or not. Can't think of a 
real use case it would be, but here's an imaginary one: before attaching 
it to a VM (or after and before running), I'd take a snapshot, then run 
the VM, do whatever, and revert before/after detaching, so the floating 
would go back to its original state.

>
>> 1. I don't see why a disk name should be unique. I don't think it's
>> enforceable under any normal circumstances: If user A decided to call
>> his disk 'system', user B who is completely unaware of A cannot call
>> his
>> disk 'system' ? It should be unique at some level, but not
>> system-wide.
> The enforcement for uniqueness has been suggested for avoiding a list of
> duplicate named disks in the Disks main tab and for identifying a specific disk.

Understood, but it's not good enough. Need to solve this, as it's not 
practical to ask me not to share a property with you - which both us do 
not really share.

> Probelm is that any disk theoretically can be floating, so you cannot differentiate between the disks using the VM name to which it is attached, for example (moreover, some of the disks in the system are shared, so which VM name will you use?...)

The fact VM names are unique is also an annoying, problematic issue, but 
I imagine there are less VMs than disks, and most are going to be FQDN 
based anyway. 'system' and 'data' are quite common names for disks, 
whereas VM names might be more original. Anyway, both don't scale.

> Maybe we can use some other attribute for identification?

The real identification can be done via the serial number, no harm in 
displaying that cryptic ID in the UI. Makes us look professional. Of 
course, it makes more sense to use the volume UUID. May come handy in 
locating it physically on disk, if it exists.


>
>> 2. I'm not sure I understand why exporting a floating disk is 'not
>> supported'. In the current design? implementation? ever?
> Currently, Export is done in a VM/Template level. Support in export/import (floating) disks is a new functionality which requires additional thinking/design/etc.

Right, so lets add 'currently not supported'.
Y.

>
>> Y.
>>