On 05/02/2015 06:19 AM, Vladimir Mosgalin wrote:
> Hi ToddAndMargo!
>
>   On 2015.05.02 at 02:00:20 -0700, ToddAndMargo wrote next:
>
>> That is what I thought.  But when I allocated a 40 GB
>> several times using both methods, ls gave me the full
>> size.  What am I missing?
>
> Either 1) your storage backend doesn't support sparse images or 2) you
> are using wrong method to check image size.
>
> Example of 1) is LVM on older systems that don't support
> thin-provisioned devices. You create 40GB volume - it's allocated right
> away. (new system, at least EL7 based libvirt should be able to create
> thin-provisioned LVM as well)
>
> Example of 2) is file backend in RAW format. It's just a full disk
> image, so reported file size is just as requested (40GB). ls -l will
> show you that. It's a sparse file, so it doesn't take that much disk
> space. du -s will show you the actual size it takes. In other words,
> it doesn't have the full size, it just seems like it does.
>
> If you're using advanced storage format like qcow, you won't see 40GB
> size at all.
>
> Note that unless you're backed up by SSD storage and need performance,
> you really should consider always using preallocated images. Sparse
> images add extra fragmentation.

Hi Vladimir,

That explains it:

        $ ls -l KVM-W10.img
        -rw-------. 1 root root 42949672960 May  1 23:04 KVM-W10.img

        $ du KVM-W10.img
        8162316 KVM-W10.img

I was looking at the requested size, not the actual size.

>
>>>> 3) What is the difference between and IDE and a Virtio
>>>>    disk?  It the Virtio disk any faster?
>>>>
>>>> Many thanks,
>>>> -T
>>
>>> It can be: the guest operating system has to support the drivers for
>>> it, and not all older operating systems do.
>>
>> So, we are basically talking about a Linux OS.  And a second
>> drive on Windows if the guest additions will install.
>
> Second drive?
> You install windows right away on system with virtio drivers (disk &
> network), just install with virtio-win drivers iso mounted use "add
> driver" (or w/e it's called). You can add all drivers (virtio, scsi,
> network, serial, balloon) this way during installation.
>
> Note that "virtio" is a somewhat deprecated disk interface, the new one
> caled virtio-scsi (for that, specify disk type as "scsi", not virtio),
> it offers more features, sometimes superior performance and (maybe most
> important) UNMAP support, which is very effective when your storage is
> backed by SSD or thinly-provisioned device. Works like a charm - e.g.
> you delete files on windows, run "optimize drive" and you can see that
> thinly-provisioned disk takes less space after that. Of course, you
> should never mess with this if you're using preallocated images on a
> regular HDD.
>

Now this is embarrassing.  I forgot I could add the ISO as a
driver during Windows install.

Thank you for helping me with this!

-T

-- 
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Computers are like air conditioners.
They malfunction when you open windows
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