Richard Laager wrote:
> By default, `zfs create -V ...` reserves space for the entire volsize,
> plus some extra (which attempts to account for overhead).
>
> If `zfs create -s -V ...` is used instead, zvols are (fully) sparse.
>
> A middle ground (partial allocation) can be achieved with
> `zfs create -s -o refreservation=... -V ...`. Both libvirt and ZFS
> support this approach, so the ZFS storage backend should support it.
Hi!
Thanks for the patch! Some questions inline.
> Signed-off-by: Richard Laager <rlaager@xxxxxxxxxx>
> ---
> src/storage/storage_backend_zfs.c | 31 +++++++++++++++++++++++++++++--
> 1 file changed, 29 insertions(+), 2 deletions(-)
>
> diff --git a/src/storage/storage_backend_zfs.c b/src/storage/storage_backend_zfs.c
> index 2e6e407..6dc3cec 100644
> --- a/src/storage/storage_backend_zfs.c
> +++ b/src/storage/storage_backend_zfs.c
> @@ -112,7 +112,7 @@ virStorageBackendZFSParseVol(virStoragePoolObjPtr pool,
> if (!(tokens = virStringSplitCount(volume_string, "\t", 0, &count)))
> return -1;
>
> - if (count != 2)
> + if (count != 3)
> goto cleanup;
>
> if (!(name_tokens = virStringSplit(tokens[0], "/", 2)))
> @@ -151,6 +151,20 @@ virStorageBackendZFSParseVol(virStoragePoolObjPtr pool,
> goto cleanup;
> }
>
> + if (virStrToLong_ull(tokens[2], NULL, 10, &volume->target.allocation) < 0) {
> + virReportError(VIR_ERR_INTERNAL_ERROR,
> + "%s", _("malformed refreservation reported"));
> + goto cleanup;
> + }
> + if (volume->target.allocation >= volume->target.capacity) {
> + /* A zvol created without -s will have a refreservation slightly larger
> + * than volblocksize.
> + */
> + volume->target.allocation = volume->target.capacity;
What if allocation specified will be much larger than capacity?
Neither zfs nor virStorageBackendZFSCreateVol() prevent from creating a
volume with:
--capacity 2G --allocation 4G
Though it'll be displayed as capacity == allocation == 2G by libvirt.
What's the reason to limit displayed allocation?
PS I noticed that it could be an issue to set refreservation larger than
volsize with ZFS on Linux:
https://github.com/zfsonlinux/zfs/issues/2468.
The issue is still open and at this moment I cannot check if I can
reproduce that on Linux.
Thanks,
> + } else {
> + volume->target.sparse = true;
> + }
> +
> if (is_new_vol &&
> VIR_APPEND_ELEMENT(pool->volumes.objs,
> pool->volumes.count,
> @@ -190,7 +204,7 @@ virStorageBackendZFSFindVols(virStoragePoolObjPtr pool,
> cmd = virCommandNewArgList(ZFS,
> "list", "-Hp",
> "-t", "volume", "-r",
> - "-o", "name,volsize",
> + "-o", "name,volsize,refreservation",
> pool->def->source.name,
> NULL);
> virCommandSetOutputBuffer(cmd, &volumes_list);
> @@ -320,15 +334,28 @@ virStorageBackendZFSCreateVol(virConnectPtr conn ATTRIBUTE_UNUSED,
> goto cleanup;
> /**
> * $ zfs create -o volmode=dev -V 10240K test/volname
> + * $ zfs create -o volmode=dev -s -V 10240K test/volname
> + * $ zfs create -o volmode=dev -s -o refreservation=1024K -V 10240K test/volname
> *
> * -o volmode=dev -- we want to get volumes exposed as cdev
> * devices. If we don't specify that zfs
> * will lookup vfs.zfs.vol.mode sysctl value
> + * -s -- create a sparse volume
> + * -o refreservation -- reserve the specified amount of space
> * -V -- tells to create a volume with the specified size
> */
> cmd = virCommandNewArgList(ZFS, "create", NULL);
> if (volmode_needed)
> virCommandAddArgList(cmd, "-o", "volmode=dev", NULL);
> + if (vol->target.capacity != vol->target.allocation) {
> + virCommandAddArg(cmd, "-s");
> + if (vol->target.allocation > 0) {
> + virCommandAddArg(cmd, "-o");
> + virCommandAddArgFormat(cmd, "refreservation=%lluK",
> + VIR_DIV_UP(vol->target.allocation, 1024));
> + }
> + vol->target.sparse = true;
> + }
> virCommandAddArg(cmd, "-V");
> virCommandAddArgFormat(cmd, "%lluK",
> VIR_DIV_UP(vol->target.capacity, 1024));
> --
> 2.1.4
>
> --
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> libvir-list@xxxxxxxxxx
> https://www.redhat.com/mailman/listinfo/libvir-list
Roman Bogorodskiy
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