openstack/diskimage-builder
Code Issues Proposed changes

Reduce LVM extent usage

Browse Source 
With 4k disks, it appears that we can encounter cases where
logical block sizes being larger begins to chip away at space
at the beginning *and* end of an LVM Physical Volume (PV).

With GPT, a similar issue occurs, larger logical block sizes
increases the number of bytes used at the beginning and end
of disk for metadata storage.

For the PV, the signature is on the second logical block, and
there is also reference to a potential backup at the end of the
volume. Which means the overall available space goes from just
being impacted by 1kB to at least 8kB. This can then begin to
impact overall alignment which is in 4MB blocks on top of the
base device.

The attempt here is to dial the sizing back just a little bit,
so we avoid assumptions regarding volume sizing ever possibly
conflicting or cases where we somehow end up asking to grow a
volume on a physical volume group which exceeds the number of
extents LVM has calculated.

Example failure this intends to avoid similar errors on a 4k
disk when growvols is triggered:

Exception: Running command failed: cmd "lvextend -L+952065064960B /dev/mapper/vg-lv_thinpool /dev/sdc6"

Which involves Standard Error ouptut along the lines of:

"Insufficient free space: 226990 extents needed, but only 226988 available"

With this change, we will apply logic to *both* the extent size
of the thinpool, if any, and all logical volumes which effectively
reduces the leveraged volumes by 8MB or two LVM extents, because
growvols tries to convert the user's preference of size or percentage
to bytes, which doesn't compensate for the additional lost extents on
a 4k block device.

Change-Id: I303d504f3c822fd534f3e3642d85873ba30d3f68
This commit is contained in:
Julia Kreger 2024-09-30 13:42:03 -07:00
parent 527f049a31
commit f764e5b520
2 changed files with 69 additions and 16 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

32
diskimage_builder/elements/growvols/static/usr/local/sbin/growvols
View File

@ -191,6 +191,31 @@ def convert_bytes(num):
return "%d%s" % (unit_num, x)
def shrink_bytes_for_alignment(num):
"""Shrink the amount of bytes to line up with LVM.
The purpose of this method is to gently shrink the requested volume
size of bytes to ensure that the size of the bytes range is in alignment
with the LVM extent size, and that the bytes value used is modeled in
the concept of extents where *two* extents have also been removed from
the value to account for any possible structural alignment differences
due to varying block sizes. In other words, reduce the size slightly to
account for the differences.
:param: num as in the number of bytes desired.
:returns: The closest value accounting for extent sizing *minus* two LVM
extents.
"""
result = ((num // PHYSICAL_EXTENT_BYTES) - 2) * PHYSICAL_EXTENT_BYTES
if result <= 0:
raise Exception(
'Not enough space available to shrink to alignment. '
'Requires more than %s, requested: %s' % (
convert_bytes(PHYSICAL_EXTENT_BYTES * 2),
convert_bytes(num)))
return result
def execute(cmd):
"""Run a command"""
LOG.info('Running: %s', printable_cmd(cmd))
@ -542,7 +567,8 @@ def main(argv):
devname = find_next_device_name(devices, disk, partnum)
thin_pool, thin_pool_name = find_thin_pool(devices, group)
if thin_pool:
# reserve for the size of the metadata volume
# reserve for the size of the metadata volume, which
# is *allocated* from the underlying storage as well.
size_bytes -= POOL_METADATA_SIZE
# reserve for the size of the spare metadata volume,
# used for metadata check and repair
@ -598,7 +624,7 @@ def main(argv):
convert_bytes(POOL_METADATA_SIZE), thin_pool)))
commands.append(Command([
'lvextend',
'-L+%sB' % size_bytes,
'-L+%sB' % shrink_bytes_for_alignment(size_bytes),
thin_pool,
dev_path
], 'Add %s to thin pool %s' % (convert_bytes(size_bytes),
@ -609,7 +635,7 @@ def main(argv):
extend_args = [
'lvextend',
'--size',
'+%sB' % size_bytes,
'+%sB' % shrink_bytes_for_alignment(size_bytes),
volume_path
]
if not thin_pool:

51
diskimage_builder/elements/growvols/tests/test_growvols.py
View File

@ -279,6 +279,33 @@ class TestGrowvols(base.BaseTestCase):
self.assertEqual('2GiB', growvols.convert_bytes(3000000000))
self.assertEqual('3725GiB', growvols.convert_bytes(4000000000000))
def test_shrink_bytes_for_alignment(self):
peb = growvols.PHYSICAL_EXTENT_BYTES
half_peb = peb // 2
# shrink 3 extents to 1
self.assertEqual(peb, growvols.shrink_bytes_for_alignment(peb * 3))
# shrink 4.5 extents to 2 (round down to whole extent minus 2 extents)
self.assertEqual(peb * 2,
growvols.shrink_bytes_for_alignment(
peb * 4 + half_peb))
# error shrinking zero
e = self.assertRaises(Exception,
growvols.shrink_bytes_for_alignment, 0)
self.assertIn('Requires more than 8MiB, requested: 0B', str(e))
# error shrinking 1 extent
e = self.assertRaises(Exception,
growvols.shrink_bytes_for_alignment, peb)
self.assertIn('Requires more than 8MiB, requested: 4MiB', str(e))
# error shrinking 2 extents
e = self.assertRaises(Exception,
growvols.shrink_bytes_for_alignment, peb * 2)
self.assertIn('Requires more than 8MiB, requested: 8MiB', str(e))
@mock.patch('subprocess.Popen')
def test_execute(self, mock_popen):
mock_process = mock.Mock()
@ -728,7 +755,7 @@ class TestGrowvols(base.BaseTestCase):
mock.call(['partprobe']),
mock.call(['pvcreate', '-ff', '--yes', '/dev/sda5']),
mock.call(['vgextend', 'vg', '/dev/sda5']),
mock.call(['lvextend', '--size', '+209404821504B',
mock.call(['lvextend', '--size', '+209396432896B',
'/dev/mapper/vg-lv_root', '/dev/sda5']),
mock.call(['xfs_growfs', '/dev/mapper/vg-lv_root'])
])
@ -759,11 +786,11 @@ class TestGrowvols(base.BaseTestCase):
mock.call(['partprobe']),
mock.call(['pvcreate', '-ff', '--yes', '/dev/sda5']),
mock.call(['vgextend', 'vg', '/dev/sda5']),
mock.call(['lvextend', '--size', '+41880125440B',
mock.call(['lvextend', '--size', '+41871736832B',
'/dev/mapper/vg-lv_home', '/dev/sda5']),
mock.call(['lvextend', '--size', '+83760250880B',
mock.call(['lvextend', '--size', '+83751862272B',
'/dev/mapper/vg-lv_var', '/dev/sda5']),
mock.call(['lvextend', '--size', '+83764445184B',
mock.call(['lvextend', '--size', '+83756056576B',
'/dev/mapper/vg-lv_root', '/dev/sda5']),
mock.call(['xfs_growfs', '/dev/mapper/vg-lv_home']),
mock.call(['xfs_growfs', '/dev/mapper/vg-lv_var']),
@ -832,13 +859,13 @@ class TestGrowvols(base.BaseTestCase):
mock.call(['vgextend', 'vg', '/dev/sda5']),
mock.call(['lvextend', '--poolmetadatasize', '+1073741824B',
'vg/lv_thinpool']),
mock.call(['lvextend', '-L+207253143552B',
mock.call(['lvextend', '-L+207244754944B',
'/dev/mapper/vg-lv_thinpool', '/dev/sda5']),
mock.call(['lvextend', '--size', '+41448112128B',
mock.call(['lvextend', '--size', '+41439723520B',
'/dev/mapper/vg-lv_home']),
mock.call(['lvextend', '--size', '+82900418560B',
mock.call(['lvextend', '--size', '+82892029952B',
'/dev/mapper/vg-lv_var']),
mock.call(['lvextend', '--size', '+82904612864B',
mock.call(['lvextend', '--size', '+82896224256B',
'/dev/mapper/vg-lv_root']),
mock.call(['xfs_growfs', '/dev/mapper/vg-lv_home']),
mock.call(['xfs_growfs', '/dev/mapper/vg-lv_var']),
@ -881,13 +908,13 @@ class TestGrowvols(base.BaseTestCase):
mock.call(['vgextend', 'vg', '/dev/mapper/mpatha6']),
mock.call(['lvextend', '--poolmetadatasize', '+1073741824B',
'vg/lv_thinpool']),
mock.call(['lvextend', '-L+207253143552B',
mock.call(['lvextend', '-L+207244754944B',
'/dev/mapper/vg-lv_thinpool', '/dev/mapper/mpatha6']),
mock.call(['lvextend', '--size', '+41448112128B',
mock.call(['lvextend', '--size', '+41439723520B',
'/dev/mapper/vg-lv_home']),
mock.call(['lvextend', '--size', '+82900418560B',
mock.call(['lvextend', '--size', '+82892029952B',
'/dev/mapper/vg-lv_var']),
mock.call(['lvextend', '--size', '+82904612864B',
mock.call(['lvextend', '--size', '+82896224256B',
'/dev/mapper/vg-lv_root']),
mock.call(['xfs_growfs', '/dev/mapper/vg-lv_home']),
mock.call(['xfs_growfs', '/dev/mapper/vg-lv_var']),