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ZFS: Support sparse volumes

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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.

Signed-off-by: Richard Laager <rlaager@wiktel.com>
This commit is contained in:
Richard Laager 2016-03-24 00:11:11 -05:00 committed by Roman Bogorodskiy
parent 727a3c5860
commit c81bba4f6f
1 changed files with 24 additions and 2 deletions
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26
src/storage/storage_backend_zfs.c
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@ -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 +151,15 @@ 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)
volume->target.sparse = true;
if (is_new_vol &&
VIR_APPEND_ELEMENT(pool->volumes.objs,
pool->volumes.count,
@ -190,7 +199,7 @@ 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);
@ -323,15 +332,28 @@ 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));