Re: [ovirt-devel] In-place sparsify support in VDSM

On Tue, May 17, 2016 at 09:50:07PM +0300, Nir Soffer wrote: > On Tue, May 17, 2016 at 7:14 PM, Shmuel Melamud <smelamud(a)redhat.com&gt; wrote: > > > Hi! > > > > There is an RFE being implemented currently ( > > https://bugzilla.redhat.com/show_bug.cgi?id=734120) to use --inplace > > option in virt-sparsify to sparsify a disk image in-place, without copying > > it. > > > > The problem is that in-place sparsify works on NFS only starting from NFS > > 4.2, while the copying implementation supposedly works with any storage. > > > > From my point of view, it is better to remove the old code and start with > > the new code that uses --inplace and just add to document that one will > > need NFS >= 4.2 for sparsify feature to work. Although the old > > implementation exists, it is not used currently so there are no actual > > users that may be affected by the change. If it will be a crying need to > > use sparsify on older NFS or some other incompatible storage, we can add it > > later on the base of the new code. The old code is far from ideal and we > > will need to rewrite it in any case, and there is not sense to do this > > without real need. > > > > Richard, > > Currently vdsm is using: > > virt-sparsify --tmp prebuilt:tmp_vol --format src_format --convert > dst_format src_vol dst_vol > (--format and --dst_format are optional) > > tmp_vol, src_vol, and dst_vol can be either file on nfs/glusterfs/other > posix shared filesystem, > or an lv created on top of lun (iscsi/fc). > > can you confirm this method works on all the storage types I mentioned? or > this depends > on the underlying storage server? Copying mode requires that the dst_vol supports sparseness. The most common case where this would *not* be true is partitions on local hard disks. You can't make a partition and/or local hard disk sparse. However all of the ones you've mentioned above support sparseness, so you should be good. *If* you were using --inplace only, you could nuke the --tmp option, and indeed all the code associated with "prebuilt" qcow2 files for scratch space. That's because --inplace mode uses hardly any temporary storage, so you can just have it use regular /var/tmp or $TMPDIR. However ... > The new inplace method is much nicer, but something that works only on > latest NFS version > is not useful for our most important users, using block storage. ... it's a shame, but yes. Rich.