[Libguestfs] [Qemu-devel] [qemu-img] support for XVA

[Tomáš Golembiovský]

On Thu, 16 Nov 2017 13:56:16 +0100
Tomáš Golembiovský <tgolembi at redhat.com> wrote:

> On Wed, 15 Nov 2017 21:41:20 +0100
> Gandalf Corvotempesta <gandalf.corvotempesta at gmail.com> wrote:
> 
> > 2017-11-15 21:29 GMT+01:00 Richard W.M. Jones <rjones at redhat.com>:  
> > > Gandalf, is there an XVA file publically available (pref. not
> > > too big) that we can look at?  
> > 
> > I can try to provide one, but it's simple:
> > 
> > # tar tvf 20160630_124823_aa72_.xva.gz | head -n 50
> > ---------- 0/0           42353 1970-01-01 01:00 ova.xml
> > ---------- 0/0         1048576 1970-01-01 01:00 Ref:175/00000000
> > ---------- 0/0              40 1970-01-01 01:00 Ref:175/00000000.checksum
> > ---------- 0/0         1048576 1970-01-01 01:00 Ref:175/00000001
> > ---------- 0/0              40 1970-01-01 01:00 Ref:175/00000001.checksum
> > ---------- 0/0         1048576 1970-01-01 01:00 Ref:175/00000003
> > ---------- 0/0              40 1970-01-01 01:00 Ref:175/00000003.checksum
> > ---------- 0/0         1048576 1970-01-01 01:00 Ref:175/00000004
> > ---------- 0/0              40 1970-01-01 01:00 Ref:175/00000004.checksum
> > ---------- 0/0         1048576 1970-01-01 01:00 Ref:175/00000005
> > ---------- 0/0              40 1970-01-01 01:00 Ref:175/00000005.checksum
> > ---------- 0/0         1048576 1970-01-01 01:00 Ref:175/00000006
> > ---------- 0/0              40 1970-01-01 01:00 Ref:175/00000006.checksum
> > ---------- 0/0         1048576 1970-01-01 01:00 Ref:175/00000007
> > ---------- 0/0              40 1970-01-01 01:00 Ref:175/00000007.checksum
> > ---------- 0/0         1048576 1970-01-01 01:00 Ref:175/00000009
> > ---------- 0/0              40 1970-01-01 01:00 Ref:175/00000009.checksum
> > ---------- 0/0         1048576 1970-01-01 01:00 Ref:175/00000010
> > ---------- 0/0              40 1970-01-01 01:00 Ref:175/00000010.checksum
> > 
> > 
> > You can ignore the ova.xml and just use the "Ref:175" directory.
> > Inside the XVA you'll fine one "Ref" directory for each virtual disk
> > (ref number is different for each disk)
> > Inside each Ref directory, you'll get tons of 1MB file, corrisponding
> > to the RAW image.
> > You have to merge these files in a single raw file with just an
> > exception: numbers are not sequential.
> > as you can see above, we have: 00000000, 00000001, 00000003
> > 
> > The 00000002 is missing, because it's totally blank. XenServer doesn't
> > export any empty block, thus it will skip the corrisponding 1MB file.
> > When building the raw image, you have to replace empty blocks with 1MB
> > full of zeros.
> > 
> > This is (in addition to the tar extract) the most time-consuming part.
> > Currently I'm rebuilding a 250GB image, with tons of files to be
> > merge.
> > If qemu-img can be patched to automatically convert this kind of
> > format, I can save about 3 hours (30 minutes for extracting the
> > tarball, and about 2 hours to merge 250-300GB image)
> >   
> 
> Hi,
> 
> I like what Richard and Max came up with. Pretty nifty solutions.
> While there's nothing wrong with them I decided to take my own shot at
> it. Since the blocks in tar file are pieces of raw image there is no
> conversion happening. All in all it's just moving bytes from one place
> to another. That means there shouldn't be a need for any heavy
> machinery, right? :)
> 
> Attached is a shell script that uses dd to do the byte-shuffling.
> I'm pretty sure this could even be safely parallelized by running
> multiple instances of dd at the same time (e.g. with xargs). But I did
> not try that.

Oh yes, and one more thing: as with the other solutions I didn't bother
reading the XML for the target size. So resize may be necessary
afterwards.

    Tomas

-- 
Tomáš Golembiovský <tgolembi at redhat.com>