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Example:
~> lvconvert --type raid1 -m 1 vg/lv
The following steps are performed to convert linear to RAID1:
1) Allocate a metadata device from the same PV as the linear device
to provide the metadata/data LV pair required for all RAID components.
2) Allocate the required number of metadata/data LV pairs for the
remaining additional images.
3) Clear the metadata LVs. This performs a LVM metadata update.
4) Create the top-level RAID LV and add the component devices.
We want to make any failure easy to unwind. This is why we don't create the
top-level LV and add the components until the last step. Should anything
happen before that, the user could simply remove the unnecessary images. Also,
we want to ensure that the metadata LVs are cleared before forming the array to
prevent stale information from polluting the new array.
A new macro 'seg_is_linear' was added to allow us to distinguish linear LVs
from striped LVs.
This patch allows a mirror to be extended without an initial resync of the
extended portion. It compliments the existing '--nosync' option to lvcreate.
This action can be done implicitly if the mirror was created with the '--nosync'
option, or explicitly if the '--nosync' option is used when extending the device.
Here are the operational criteria:
1) A mirror created with '--nosync' should extend with 'nosync' implicitly
[EXAMPLE]# lvs vg; lvextend -L +5G vg/lv ; lvs vg
LV VG Attr LSize Pool Origin Snap% Move Log Copy% Convert
lv vg Mwi-a-m- 5.00g lv_mlog 100.00
Extending 2 mirror images.
Extending logical volume lv to 10.00 GiB
Logical volume lv successfully resized
LV VG Attr LSize Pool Origin Snap% Move Log Copy% Convert
lv vg Mwi-a-m- 10.00g lv_mlog 100.00
2) The 'M' attribute ('M' signifies a mirror created with '--nosync', while 'm'
signifies a mirror created w/o '--nosync') must be preserved when extending a
mirror created with '--nosync'. See #1 for example of 'M' attribute.
3) A mirror created without '--nosync' should extend with 'nosync' only when
'--nosync' is explicitly used when extending.
[EXAMPLE]# lvs vg; lvextend -L +5G vg/lv; lvs vg
LV VG Attr LSize Pool Origin Snap% Move Log Copy% Convert
lv vg mwi-a-m- 20.00m lv_mlog 100.00
Extending 2 mirror images.
Extending logical volume lv to 5.02 GiB
Logical volume lv successfully resized
LV VG Attr LSize Pool Origin Snap% Move Log Copy% Convert
lv vg mwi-a-m- 5.02g lv_mlog 0.39
vs.
[EXAMPLE]# lvs vg; lvextend -L +5G vg/lv --nosync; lvs vg
LV VG Attr LSize Pool Origin Snap% Move Log Copy% Convert
lv vg mwi-a-m- 20.00m lv_mlog 100.00
Extending 2 mirror images.
Extending logical volume lv to 5.02 GiB
Logical volume lv successfully resized
LV VG Attr LSize Pool Origin Snap% Move Log Copy% Convert
lv vg Mwi-a-m- 5.02g lv_mlog 100.00
4) The 'm' attribute must change to 'M' when extending a mirror created without
'--nosync' is extended with the '--nosync' option. (See #3 examples above.)
5) An inactive mirror's sync percent cannot be determined definitively, so it
must not be allowed to skip resync. Instead, the extend should ask the user if
they want to extend while performing a resync.
[EXAMPLE]# lvchange -an vg/lv
[EXAMPLE]# lvextend -L +5G vg/lv
Extending 2 mirror images.
Extending logical volume lv to 10.00 GiB
vg/lv is not active. Unable to get sync percent.
Do full resync of extended portion of vg/lv? [y/n]: y
Logical volume lv successfully resized
6) A mirror that is performing recovery (as opposed to an initial sync) - like
after a failure - is not allowed to extend with either an implicit or
explicit nosync option. [You can simulate this with a 'corelog' mirror because
when it is reactivated, it must be recovered every time.]
[EXAMPLE]# lvcreate -m1 -L 5G -n lv vg --nosync --corelog
WARNING: New mirror won't be synchronised. Don't read what you didn't write!
Logical volume "lv" created
[EXAMPLE]# lvs vg
LV VG Attr LSize Pool Origin Snap% Move Log Copy% Convert
lv vg Mwi-a-m- 5.00g 100.00
[EXAMPLE]# lvchange -an vg/lv; lvchange -ay vg/lv; lvs vg
LV VG Attr LSize Pool Origin Snap% Move Log Copy% Convert
lv vg Mwi-a-m- 5.00g 0.08
[EXAMPLE]# lvextend -L +5G vg/lv
Extending 2 mirror images.
Extending logical volume lv to 10.00 GiB
vg/lv cannot be extended while it is recovering.
7) If 'no' is selected in #5 or if the condition in #6 is hit, it should not
result in the mirror being resized or the 'm/M' attribute being changed.
NOTE: A mirror created with '--nosync' behaves differently than one created
without it when performing an extension. The former cannot be extended when
the mirror is recovering (unless in-active), while the latter can. This is
a reasonable thing to do since recovery of a mirror doesn't take long (at
least in the case of an on-disk log) and it would cause far more time in
degraded mode if the extension w/o '--nosync' was allowed. It might be
reasonable to add the ability to force the operation in the future. This
should /not/ force a nosync extension, but rather force a sync'ed extension.
IOW, the user would be saying, "Yes, yes... I know recovery won't take long
and that I'll be adding significantly to the time spent in degraded mode, but
I need the extra space right now!".
This patch also does some clean-up of the splitmirrors code.
I've attempted to clean-up the splitmirrors code to make it easier to
understand with fewer operations. I've tried to reduce the number of
metadata operations without compromising the intermediate stages which
are necessary for easy clean-up in the even of failure.
These changes now correctly handle cluster situations - including exclusive
cluster mirrors. Whereas before, a splitmirror operation would result in
remote nodes having LVM commands report the newly split LV with a proper
name while DM commands would report the old (pre-split) names of the device.
IOW, there was a kernel/userspace mismatch.
The original commit comments can be located via this git commit ID:
7d8e615c0b
There were three possible solutions to the original problem proposed in the
initial check-in. The one chosen was as follows:
2) Do like _remove_mirror_images does and suspend the original, then suspend
the sub-lv (the error target), then resume the sub-lv, and finally resume the
original LV. This seems like extra pointless operations to me, but it doesn't
produce the error message (although, I'm not sure why) and it allows us to
leave the visible flag in place.
Turns out, the cluster also views the extra suspend/resume operations as
pointless too and ignores them. So, this solution doesn't work in a cluster.
Further, I've noticed that in addition to the remote cluster nodes still getting
I/O errors from scanning the error target, they also have a different LVM and
DM views of the same LV. IOW, while the LVM level (gotten from the LVM metadata)
sees the correct name for the newly split LV, device-mapper still maintains the
old names.
Because the original fix failed to completely fix the problem (or work-around it)
and because a better solution must be found to address the additional cluster
issue of device renaming, I am reverting the above mentioned commit.
The current code does not always assign proper udev flags to sub-LVs (e.g.
mirror images and log LVs). This shows up especially during a splitmirror
operation in which an image is split off from a mirror to form a new LV.
A mirror with a disk log is actually composed of 4 different LVs: the 2
mirror images, the log, and the top-level LV that "glues" them all together.
When a 2-way mirror is split into two linear LVs, two of those LVs must be
removed. The segments of the image which is not split off to form the new
LV are transferred to the top-level LV. This is done so that the original
LV can maintain its major/minor, UUID, and name. The sub-lv from which the
segments were transferred gets an error segment as a transitory process
before it is eventually removed. (Note that if the error target was not put
in place, a resume_lv would result in two LVs pointing to the same segment!
If the machine crashes before the eventual removal of the sub-LV, the result
would be a residual LV with the same mapping as the original (now linear) LV.)
So, the two LVs that need to be removed are now the log device and the sub-LV
with the error segment. If udev_flags are not properly set, a resume will
cause the error LV to come up and be scanned by udev. This causes I/O errors.
Additionally, when udev scans sub-LVs (or former sub-LVs), it can cause races
when we are trying to remove those LVs. This is especially bad during failure
conditions.
When the mirror is suspended, the top-level along with its sub-LVs are
suspended. The changes (now 2 linear devices and the yet-to-be-removed log
and error LV) are committed. When the resume takes place on the original
LV, there are no longer links to the other sub-lvs through the LVM metadata.
The links are implicitly handled by querying the kernel for a list of
dependencies. This is done in the '_add_dev' function (which is recursively
called for each dependency found) - called through the following chain:
_add_dev
dm_tree_add_dev_with_udev_flags
<*** DM / LVM divide ***>
_add_dev_to_dtree
_add_lv_to_dtree
_create_partial_dtree
_tree_action
dev_manager_activate
_lv_activate_lv
_lv_resume
lv_resume_if_active
When udev flags are calculated by '_get_udev_flags', it is done by referencing
the 'logical_volume' structure. Those flags are then passed down into
'dm_tree_add_dev_with_udev_flags', which in turn passes them to '_add_dev'.
Unfortunately, when '_add_dev' is finding the dependencies, it has no way to
calculate their proper udev_flags. This is because it is below the DM/LVM
divide - it doesn't have access to the logical_volume structure. In fact,
'_add_dev' simply reuses the udev_flags given for the initial device! This
virtually guarentees the udev_flags are wrong for all the dependencies unless
they are reset by some other mechanism. The current code provides no such
mechanism. Even if '_add_new_lv_to_dtree' were called on the sub-devices -
which it isn't - entries already in the tree are simply passed over, failing
to reset any udev_flags. The solution must retain its implicit nature of
discovering dependencies and be able to go back over the dependencies found
to properly set the udev_flags.
My solution simply calls a new function before leaving '_add_new_lv_to_dtree'
that iterates over the dtree nodes to properly reset the udev_flags of any
children. It is important that this function occur after the '_add_dev' has
done its job of querying the kernel for a list of dependencies. It is this
list of children that we use to look up their respective LVs and properly
calculate the udev_flags.
This solution has worked for single machine, cluster, and cluster w/ exclusive
activation.
Make limits for thin data_block_size and device_id part of public API.
FIXME: read them possible from some kernel header file in the future ?
But we may need to support different values for different versions ?
Before, we used to display "Can't remove open logical volume" which was
generic. There 3 possibilities of how a device could be opened:
- used by another device
- having a filesystem on that device which is mounted
- opened directly by an application
With the help of sysfs info, we can distinguish the first two situations.
The third one will be subject to "remove retry" logic - if it's opened
quickly (e.g. a parallel scan from within a udev rule run), this will
finish quickly and we can remove it once it has finished. If it's a
legitimate application that keeps the device opened, we'll do our best
to remove the device, but we will fail finally after a few retries.
seg->areas and seg->meta_areas. We also need to copy the memory from the
old arrays to the newly allocated arrays. The amount of memory to copy was
determined by seg->area_count. However, seg->area_count was being set to the
higher value after copying the 'seg->areas' information, but before copying
the 'seg->meta_areas' information. This means we were copying more memory
than necessary for 'seg->meta_areas' - something that could lead to a segfault.
Compiler says variable may be used uninitialized. It can't be, but we
initialize the variable to NULL anyway. Also, remove the double initialization
of another variable.
This bug showed up when trying to add a log to a mirror whose images are on
multiple devices. This is an intra-release regression and no WHATS_NEW
entry will be added. The error was introduce in the following commit:
2d8a2f35c7
The solution is to recognise in _alloc_init that if there are no mirrors
or stripes specified, then 'new_extents' should be zero.
to settle udev before calling deactivate_lv.
This is an intra-release regression (no WHATS_NEW entry required). It is
part of the fix for the current WHATS_NEW entry:
Work around resume_lv causing error LV scanning during splitmirror operation.
When user wants to remove thin pool - check if there are no thin volumes using it.
If so - query before removal (or -ff for no question) and remove them first.
When LV is unlinked, we want to catch problem in vg_validate,
that LV has changed.
i.e. catch LV has been removed and is no long thin_pool while still
being referenced by some thin volume.
Revert John patch, which fixed only 1 place where ~LVM_WRITE was in use and
convert ommited LVM_READ/WRITE flags to 64bit constants as well.
(Since both 'status' flags for LV and VG are 64bit.)
Changing lv_mirror_count to only count the AREA_LVs made the function
stop working for PVMOVE mirrors. A conditional has been added to fix
that problem. Additionally, when counting the images in a mirror stack,
we don't need to subtract 1 from the count we get back from the
lv_mirror_count call on the temporary mirror layer. (This is because we
are no falsely counting the top layer of the temporary mirror.)
lv_mirror_count was not able to handle mirrors of stripes properly. When a
failed device is removed, the MIRRORED status flag is removed from the LV
conditionally based on the results of lv_mirror_count. However, lv_mirror_count
trusted the MIRRORED flag - thinking any such LV must be mirrored. It would
happily assign first_seg(lv)->area_count as the number of mirrors, but when
a mirrored striped LV was reduced to a simple striped LV area_count would be
the number of /stripes/ not the number of /mirrors/. A result higher than 1
would be returned from lv_mirror_count, the MIRRORED flag would not be cleared,
and the LV would fail to be up-converted properly in lvconvert_mirrors_aux
because of it.
The operation of deactivating the residual error target LV after removing a
mirror layer can cause a "device in-use" conflict with udev. Giving udev a
poke before calling deactivate_lv eliminates the conflict. The stick used
to poke udev is 'sync_local_dev_names'.
Kernel requires a mirror to be at least 1 region large. So,
if our mirror log is itself a mirror, it must be at least
1 region large. This restriction may not be necessary for
non-mirrored logs, but we apply the rule anyway.
(The other option is to make the region size of the log
mirror smaller than the mirror it is acting as a log for,
but that really complicates things. It's much easier to
keep the region_size the same for both.)
WHATS_NEW entry:
Fix log size calculation when only a log is being added to a mirror.
The original fix pass the mirror LV to allocate_extents (rather than
passing NULL) so that _alloc_init could correctly determine the necessary
size of the mirror log. In the previous check-in, I noted:
In order to get a decent value computed, we need to pass in the 'lv' argument
to allocate_extents. This would normally imply a desire for cling/contiguous
allocation to the given LV, but since we are not allocating any parallel
extents and only log extents, it works fine.
However, passing in the LV did have unintended consequences on the placement of
the log. The better solution is to pass in the number of extext that are in
the mirror LV instead of the LV itself. This will not cause the allocator to
reserve that number of extents, because 'stripes' and 'mirrors' are specified
as 0. Thus, 'extents' is used to calculate the size of the log, but won't
affect how much is allocated.
LVM_WRITE is a 32-bit flag. Now that RAID[_IMAGE|_META] are 64-bit,
and'ing a RAID LV's status against LVM_WRITE can reset the higher order
flags.
A similar thing will affect thinp flags if not careful.
_alloc_init calculates the number of necessary log extents via
'mirror_log_extents'. 'mirror_log_extents' takes 3 arguments: region_size,
pe_size, and size of the mirror LV. Unfortunately, _alloc_init is guessing at
the mirror size by using 'ah->new_extents / ah->area_multiple' - the number of
extents that the mirror images have. However, this is /always/ wrong when
allocating the log separately. Further, the log is always allocated separately
unless we are up-converting the mirror at the same time. It was by luck alone
that a default value of '1' reflects what we want in most cases.
In order to get a decent value computed, we need to pass in the 'lv' argument
to allocate_extents. This would normally imply a desire for cling/contiguous
allocation to the given LV, but since we are not allocating any parallel
extents and only log extents, it works fine.
When an image is split from a 2-way mirror, the original mirror is converted to
a linear device. To do this, the top "layer" must be removed. The segments
are transferred from the sub-lv to the top-level LV and the link is severed.
The former sub-lv - having its segments transferred - now contains a temporary
error target.
When the original LV is resumed, the old sub-lv that now contains an error
segment is activated and scanned. This is what causes the I/O error messages.
There are three ways to fix this problem:
1) Do not set the sub-lv which contains the error target as "visible" before
suspending the original LV. This way, when the original is resumed, the sub-lv
device node is not created and it is not scanned - avoiding the error messages.
The problem with this approach is that if the machine crashes after the
resume, it leaves the *hidden* LV in place and the user has a more difficult
time noticing that it needs to be cleaned up. Thus, this type of processing is
frowned upon.
2) Do like _remove_mirror_images does and suspend the original, then suspend
the sub-lv (the error target), then resume the sub-lv, and finally resume the
original LV. This seems like extra pointless operations to me, but it does not
produce the error message (although, I'm not sure why) and it allows us to
leave the visible flag in place.
3) Flag the sub-lv (error target) with a "do not scan" flag. This seems like
the cleanest approach, but I have been unable to find the method for doing
this. LVs get tagged in such a way by _get_udev_flags, but in this case the
resume of the original LV also resumes the error target LV without running it
through _get_udev_flags (likely because they are no longer linked). Could
there be something wrong in resume_lv?
Option #2 was chosen to fix this bug, but it seems like more of a workaround
for now.
