[Libguestfs] [PATCH v7 6/6] v2v: Add -o rhv-upload output mode (RHBZ#1557273).

[Nir Soffer]

On Thu, Mar 29, 2018 at 1:59 PM Richard W.M. Jones <rjones at redhat.com>
wrote:

> I found another problem which is sort of related to this thread.  I
> hit a time-out waiting for the disk to be unlocked after creation:
>
>
> https://github.com/libguestfs/libguestfs/commit/8081f54105bd990233f166170890192c1fd7d1f3#diff-5ca47c29ae13efa3959b8b28cf4dbd31R112
> line 112
>
> The disk size in this case is 40 GB and we currently wait 5 minutes.
>
> On the ovirt-node there's an ‘fallocate’ process (still) running.
> It's taken 23 minutes so far.
>

This code is using posix_fallocate and it can be very slow on NFS < 4.2,
writing one byte to every 4k block.


> Because we didn't reach a satisfactory conclusion of the whole
> sparse/format business, I am currently setting sparse = False
> (format is always raw in my testing):
>
>
> https://github.com/libguestfs/libguestfs/commit/8081f54105bd990233f166170890192c1fd7d1f3#diff-5ca47c29ae13efa3959b8b28cf4dbd31R92
> line 92
>
> I guess this is the cause of this problem in some sense.  Is there
> something we can do?  I'm still unclear how to fix the sparse/format
> mess, it seems unsolvable from the client side because we don't have
> sufficient information to make a decision.
>

I don't think always using sparse=False is a good solution. We have an issue
only with block storage, so there is no need to force sparse=False for every
kind of storage.

I think the behavior should be:

- if the user wants raw image (sparse=False) on file domain we can warn
that
creating preallocated disk on file storage can take lot of time, and we
should
wait until the disk is ready. Or we can always use thin for upload to file
based
storage, this is what we for uploading from the UI.

- if the user wants thin image on block storage, we must allocate the entire
image when we create a disk. In 4.2.4 we will support engine API to reduce
an image to the optimal size, and you will be able to call this when you
complete
the upload.

- if the user wants thin image on file storage, or raw image on block
storage,
we don't have any issue

In 4.3 we plan to improve engine extend volume api so it will update the
ticket
size when extending a disk. With this you will be able to create a thin
disk on
block storage and extend it when needed.

Nir
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