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In order to support striped raid5/6/10 LV reshaping (change
of LV type, stripesize or number of legs), this patch
introduces local infrastructure to raid_manip.c
used by followup patches.
Add functions:
- to check reshaping is supported in target attibute
- to return device health string needed to check
the raid device is ready to reshape
Related: rhbz834579
Related: rhbz1191935
Related: rhbz1191978
In order to support striped raid5/6/10 LV reshaping (change
of LV type, stripesize or number of legs), this patch
introduces infrastructure prerequisites to be used
by raid_manip.c extensions in followup patches.
This base is needed for allocation of out-of-place
reshape space required by the MD raid personalities to
avoid writing over data in-place when reading off the
current RAID layout or number of legs and writing out
the new layout or to a different number of legs
(i.e. restripe)
Changes:
- add members reshape_len to 'struct lv_segment' to store
out-of-place reshape length per component rimage
- add member data_copies to struct lv_segment
to support more than 2 raid10 data copies
- make alloc_lv_segment() aware of both reshape_len and data_copies
- adjust all alloc_lv_segment() callers to the new API
- add functions to retrieve the current data offset (needed for
out-of-place reshaping space allocation) and the devices count
from the kernel
- make libdm deptree code aware of reshape_len
- add LV flags for disk add/remove reshaping
- support import/export of the new 'struct lv_segment' members
- enhance lv_extend/_lv_reduce to cope with reshape_len
- add seg_is_*/segtype_is_* macros related to reshaping
- add target version check for reshaping
- grow rebuilds/writemostly bitmaps to 246 bit to support kernel maximal
- enhance libdm deptree code to support data_offset (out-of-place reshaping)
and delta_disk (legs add/remove reshaping) target arguments
Related: rhbz834579
Related: rhbz1191935
Related: rhbz1191978
The MD kernel raid1 personality does no use any writemostly leg as the primary.
In case a previous linear LV holding data gets upconverted to
raid1 it becomes the primary leg of the new raid1 LV and a full
resynchronization is started to update the new legs.
No writemostly and/or writebehind setting may be allowed during
this initial, full synchronization period of this new raid1 LV
(using the lvchange(8) command), because that would change the
primary (i.e the previous linear LV) thus causing data loss.
lvchange has a bug not preventing this scenario.
Fix rejects setting writemostly and/or writebehind on resychronizing raid1 LVs.
Once we have status in the lvm2 metadata about the linear -> raid upconversion,
we may relax this constraint for other types of resynchronization
(e.g. for user requested "lvchange --resync ").
New lvchange-raid1-writemostly.sh test is added to the test suite.
Resolves: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=855895
Remove allocate_pvs from raid_manip.c:_region_size_change_request() API
and lv_extend() using it added for temporary test purpose.
Related: rhbz1366296
Add:
- region size checks to raid_manip.c types array and supporting functions
- tests to lvconvert-raid-takeover.sh to check bogus
"lvconvert --type --regionsize N " requests
Related: rhbz1366296
Add:
- conversion support from striped/raid0/raid0_meta to/from raid10;
raid10 goes by the near format (same as used in creation of
raid10 LVs), which groups data copies together with their original
blocks (e.g. 3-way striped, 2 data copies resulting in 112233 in the
first stripe followed by 445566 in the second etc.) and is limited
to even numbers of legs for now
- related tests to lvconvert-raid-takeover.sh
- typo
Related: rhbz1366296
- support shrinking of raid0/1/4/5/6/10 LVs
- enhance lvresize-raid.sh tests: add raid0* and raid10
- fix have_raid4 in aux.sh to allow lv_resize-raid.sh
and other scripts to test raid4
Resolves: rhbz1394048
Commit cfb6ef654d introduced
support to change RAID region size.
Fix:
- don't change region_size until after prompting the user
- use log_print_unless_silent() instead of log_warn()
- avoid superfluous sigint() calls which are already
covered in yes_no_prompt()
- typo
Related: rhbz1392947
Commit cfb6ef654d introduced
support to change RAID region size.
Add:
- missing conditions to support any types to function with
it in lv_raid_convert(); temporary workaround used until
cli validation patches get merged
- tests requesting "-R " to lvconvert-raid-takeover.sh
involving a cleanup of the script
Related: rhbz1392947
Cleanups as of Jons review:
- enhance comment about mandatory raid4 <-> raid5_n activation w/o metadata SubLVs
- remove bogus segment flag setting
- fix to sync related comments on conversions to raid0/striped and amongst raid4/5
- add missing error message for non-synced conversion to raid0/striped
Related: rhbz1366296
Add:
- support to change region size of existing RaidLVs
(all RAID LV types but raid0/raid0_meta)
- lvconvert-raid-regionsize.sh with test variations
for different RAID types and region sizes
Resolves: rhbz1392947
Add:
- support for segment types raid6_{ls,rs,la,ra}_6
(striped raid with dedicated last Q-Syndrome SubLVs)
- conversion support from raid5_{ls,rs,la,ra} to/from raid6_{ls,rs,la,ra}_6
- setting convenient segtypes on conversions from/to raid4/5/6
- related tests to lvconvert-raid-takeover.sh factoring
out _lvcreate,_lvconvert funxtions
Related: rhbz1366296
Add:
- support for segment type raid6_n_6 (striped raid with dedicated last parity/Q-Syndrome SubLVs)
- conversion support from striped/raid0/raid0_meta/raid4 to/from raid6_n_6
- related tests to lvconvert-raid-takeover.sh
Related: rhbz1366296
Add:
- support for segment type raid5_n (striped raid with dedicated last parity SubLVs)
- conversion support from striped/raid0/raid0_meta/raid4 to/from raid5_n
- related tests to lvconvert-raid-takeover.sh
Related: rhbz1366296
Commit 0690392040 revealed a problem
in raid metadata manipulation.
We do two operations in one table reload:
- raid leg/image extraction
- rename remaining raid legs
This should be made in separate steps. Otherwise we do an
uncorrectable table change on error path (leaving tables
for admin and dmsetup).
As a hotfix - restore the previous logic and use a single
new function _lv_update_and_reload_list which activates exclusively
extracted LVs on the list before resuming suspended raid LV.
This restore 'rename' functionality upon resume.
Also still preserve the 'origin_only' logic - although we know
it's not working properly for cluster and LV stacking.
Further fixes are needed.
backup is not 'tested' for success and also it should
actually happen just when command is finished.
We do not target to make backups with each inter-step
metadata change.
RAID is LV property
TODO: only 2 flags are seg->status: PVMOVE & MERGING
At least the second one should be soon elimanted as again
we merge LV not a segment.
This is another place for 'common' use pattern or
reload and activation of deleted devices.
(Moving the exclusive activation to _deactivate_and_remove_lvs()).
TODO: looks like halve of raid function is reloading
just 'origin' - and the other full LV.
Fix order of operation when converting raid1 into old mirror.
Before any later metadata modification are initiated prepare
mirror_log device with all clearing.
Then directly convert raid1 into mirror with mirror_log.
This convertion now properly see as precommitted metadata
new 'mirror' and committed old 'raid' and is able to
preload all LVs.
(Automatic) repair may not be allowed during the initial sync of an upconverted
linear LV, because the data on the failing, primary leg hasn't been completely
synchronized to the N-1 other legs of the raid1 LV (replacing failed legs during
repair involves discontinuing access to any replaced legs data, thus preventing
data recovery on the primary leg e.g. via dd_rescue).
Even though repair would not cause data loss when adding legs to a fully synced
raid1 LV, we don't have information yet defining this state yet (e.g. a raid1
LV flag telling the fully synchronized status before any legs were added),
hence can't automatically decide to allow to repair.
If nonetheless a repair on a non-synced raid1 LVs is intended, the "--force"
option has to be provided.
Resolves: rhbz1311765
On conversions between striped/raid0* and raid4, the kernel expects
the dedicated raid4 parity SubLVs in the first segment area rather than
in the last it's been allocated to, thus the data mapping ain't proper.
Enhance lvconvert (lib/metadata/raid_manip.c) to shift the dedicated
parity SubLVs on conversions from striped/raid0* to raid4 and vice-versa.
In case of raid0_meta -> raid4 where the MD raid0 personality already has
stored RAID array device positions in the superblocks, the MetaLVs have to
be cleared so that the kernel doesn't fail validating the array positions
after lvm has shifted them up by one.
Add more tests to lvconvert-raid-takeover.sh including one to check for
mapping flaws by converting a created raid4 with filesystem -> striped
and fsck it.
Whilst on it:
- add missing direct striped -> raid4 conversion to the takeover array
to avoid an intermim conversion from striped -> raid0*
- clean up the takeover array
- allow lvconvert to actually call lv_raid_convert() on all takeover requests
in order to check parameters and display messages provided by takeover
functions rather than just "...not supported" from within lvconvert
- fix a typo
Resolves: rhbz1386148
Works if the pool is inactive.
Activation code doesn't notice a new raid dependency in on-disk metadata
when a thin LV is already active.
https://bugzilla.redhat.com/1365286
The dm-raid target now rejects device rebuild requests during ongoing
resynchronization thus causing 'lvconvert --repair ...' to fail with
a kernel error message. This regresses with respect to failing automatic
repair via the dmeventd RAID plugin in case raid_fault_policy="allocate"
is configured in lvm.conf as well.
Previously allowing such repair request required cancelling the
resynchronization of any still accessible DataLVs, hence reasoning
potential data loss.
Patch allows the resynchronization of still accessible DataLVs to
finish up by rejecting any 'lvconvert --repair ...'.
It enhances the dmeventd RAID plugin to be able to automatically repair
by postponing the repair after synchronization ended.
More tests are added to lvconvert-rebuild-raid.sh to cover single
and multiple DataLV failure cases for the different RAID levels.
- resolves: rhbz1371717
'pvmove -n name pv1 pv2' allows to collocate multiple RAID SubLVs
on pv2 (e.g. results in collocated raidlv_rimage_0 and raidlv_rimage_1),
thus causing loss of resilence and/or performance of the RaidLV.
Fix this pvmove flaw leading to potential data loss in case of PV failure
by preventing any SubLVs from collocation on any PVs of the RaidLV.
Still allow to collocate any DataLVs of a RaidLV with their sibling MetaLVs
and vice-versa though (e.g. raidlv_rmeta_0 on pv1 may still be moved to pv2
already holding raidlv_rimage_0).
Because access to the top-level RaidLV name is needed,
promote local _top_level_lv_name() from raid_manip.c
to global top_level_lv_name().
- resolves rhbz1202497
Adding MetaLVs to given DataLVs (e.g. raid0 -> raid0_meta takeover),
_avoid_pvs_with_other_images_of_lv() was missing code to prohibit
allocation when called with a just allocated MetaLV to prohibit
collaocation of the next allocated MetaLV on the same PV.
- resolves rhbz1366738
'lvchange --resync LV' or 'lvchange --syncaction repair LV' request the
RAID layout specific parity blocks in raid4/5/6 to be recreated or the
mirrored blocks to be copied again from the master leg/copy for raid1/10,
thus not allowing a rebuild of a particular PV.
Introduce repeatable option '--[raid]rebuild PV' to allow to request
rebuilds of specific PVs in a RaidLV which are known to contain corrupt
data (e.g. rebuild a raid1 master leg).
Add test lvchange-rebuild-raid.sh to test/shell doing rebuild
variations on raid1/10 and 5; add aux function check_status_chars
to support the new test.
- Resolves rhbz1064592
Any failing stripes in raid0/raid0_meta type LVs cause data loss,
thus replacement via 'lvconvert --replace...' does not make sense.
Patch prohibits replacement on raid0/raid0_meta LVs.
- resolves rhbz1356734
An unconditional access to the non-existing MetaLV of a raid0 LV in
lv_raid_remove_missing() was causing the segfault.
Only call log_debug() on replacements of existing MetaLVs.
- resolves rhbz1354646
Skip testing target_pvs for NULL, we already
dereference it in many other places.
If check would ever be needed - it needs to be
in front of _raid_extract_images().
When kernel target reports sync status as 0% it might as well mean
it's 100% in sync, just the target is in some race inconsistent
state - so reread once again and take a more optimistic value ;)
Patch tries to work around:
https://bugzilla.redhat.com/show_bug.cgi?id=1210637
When raid leg is extracted, now the preload code handles this state
correctly and put proper new table entry into dm tree,
so the activation of extracted leg and removed metadata works
after commit.
The previous patch felt short WRT disabling allocation on PVs holding other
legs of the RAID LV persistently; this patch introduces an internal,
transient PV flag PV_ALLOCATION_PROHIBITED to address this very problem.
General problem description for completeness:
An 'lvconvert --repair $RAID_LV" to replace a failed leg of a multi-segment
RAID10/4/5/6 logical volume can lead to allocation of (parts of) the replacement
image component pair on the physical volume of another image component
(e.g. image 0 allocated on the same PV as image 1 silently impeding resilience).
Patch fixes this severe resilince issue by prohibiting allocation on PVs
already holding other legs of the RAID set. It allows to allocate free space
on any operational PV already holding parts of the image component pair.
An 'lvconvert --repair $RAID_LV" to replace a failed leg of a multi-segment
RAID10/4/5/6 logical volume can lead to allocation of (parts of) the replacement
image component pair on the physical volume of another image component
(e.g. image 0 allocated on the same PV as image 1 silently impeding resilience).
Patch fixes this severe resilince issue by prohibiting allocation on PVs
already holding other legs of the RAID set. It allows to allocate free space
on any operational PV already holding parts of the image component pair.
$ lvcreate -l1 -m1 --type mirror vg
Logical volume "lvol0" created.
$ lvconvert --type raid1 vg/lvol0
Before:
$ lvs -a vg
LV VG Active Attr LSize Cpy%Sync Layout Role
lvol0 vg active rwi-a-r--- 4.00m 100.00 raid,raid1 public
[lvol0_mimage_0_rimage_0] vg active iwi-aor--- 4.00m linear private,raid,image
[lvol0_mimage_1_rimage_1] vg active iwi-aor--- 4.00m linear private,raid,image
[lvol0_rmeta_0] vg active ewi-aor--- 4.00m linear private,raid,metadata
[lvol0_rmeta_1] vg active ewi-aor--- 4.00m linear private,raid,metadata
Incorrect name: lvol0_mimage_0_rimage_0
With this patch applied:
$ lvs -a vg
LV VG Active Attr LSize Cpy%Sync Layout Role
lvol0 vg active rwi-a-r--- 4.00m 100.00 raid,raid1 public
[lvol0_rimage_0] vg active iwi-aor--- 4.00m linear private,raid,image
[lvol0_rimage_1] vg active iwi-aor--- 4.00m linear private,raid,image
[lvol0_rmeta_0] vg active ewi-aor--- 4.00m linear private,raid,metadata
[lvol0_rmeta_1] vg active ewi-aor--- 4.00m linear private,raid,metadata
Proper name: lvol0_rimage_0
When we split leg from raid - we take a proper new lock for a new LV.
However for now activation checks only 'existince' of device UUID,
but it's not validating device has a proper name.
As a quick fix call suspend()/resume() to rename after split mirror.
Ask for lock the proper LV.
Use the top-most LV to query for locally exclusive lock.
The rest of operations are then using 'lv_info()'
TODO:
Check all devices are reloaded from proper level.
In general any query on lv_is_active is supposed to be running
ona lv_lock_holder() volume.
Instead of segtype->ops->name() introduce lvseg_name().
This also allows us to leave name() function 'empty' for default
return of segtype->name.
TODO: add functions for rest of ops->
We are not using already defined segement type names where we could.
There is a lot of other places in device-mapper and LVM2 we have those
hardcoded so we should better finally have a common interface in
libdevmapper to avoid this.
Try to enforce consistent macro usage along these lines:
lv_is_mirror - mirror that uses the original dm-raid1 implementation
(segment type "mirror")
lv_is_mirror_type - also includes internal mirror image and log LVs
lv_is_raid - raid volume that uses the new dm-raid implementation
(segment type "raid")
lv_is_raid_type - also includes internal raid image / log / metadata LVs
lv_is_mirrored - LV is mirrored using either kernel implementation
(excludes non-mirror modes like raid5 etc.)
lv_is_pvmove - internal pvmove volume
Use lv_update_and_reload() and lv_update_and_reload_origin()
to handle write/suspend/commit/resume sequence.
In few places this properly handle vg_revert() after suspend failure,
and also ensures there is metadata backup after successful vg_commit().
When repairing RAID LVs that have multiple PVs per image, allow
replacement images to be reallocated from the PVs that have not
failed in the image if there is sufficient space.
This allows for scenarios where a 2-way RAID1 is spread across 4 PVs,
where each image lives on two PVs but doesn't use the entire space
on any of them. If one PV fails and there is sufficient space on the
remaining PV in the image, the image can be reallocated on just the
remaining PV.
I've changed build_parallel_areas_from_lv to take a new parameter
that allows the caller to build parallel areas by LV vs by segment.
Previously, the function created a list of parallel areas for each
segment in the given LV. When it came time for allocation, the
parallel areas were honored on a segment basis. This was problematic
for RAID because any new RAID image must avoid being placed on any
PVs used by other images in the RAID. For example, if we have a
linear LV that has half its space on one PV and half on another, we
do not want an up-convert to use either of those PVs. It should
especially not wind up with the following, where the first portion
of one LV is paired up with the second portion of the other:
------PV1------- ------PV2-------
[ 2of2 image_1 ] [ 1of2 image_1 ]
[ 1of2 image_0 ] [ 2of2 image_0 ]
---------------- ----------------
Previously, it was possible for this to happen. The change makes
it so that the returned parallel areas list contains one "super"
segment (seg_pvs) with a list of all the PVs from every actual
segment in the given LV and covering the entire logical extent range.
This change allows RAID conversions to function properly when there
are existing images that contain multiple segments that span more
than one PV.
When down-converting a RAID1 LV, if the user specifies too few devices,
they will get a confusing message.
Ex:
[root]# lvcreate -m 2 --type raid1 -n raid -L 500M taft
Logical volume "raid" created
[root]# lvconvert -m 0 taft/raid /dev/sdd1
Unable to extract enough images to satisfy request
Failed to extract images from taft/raid
This patch makes the error message a bit clearer by telling the user
the count they are trying to remove and the number of devices they
supplied.
[root@bp-01 lvm2]# lvcreate --type raid1 -m 3 -L 200M -n lv vg
Logical volume "lv" created
[root@bp-01 lvm2]# lvconvert -m -3 vg/lv /dev/sdb1
Unable to remove 3 images: Only 1 device given.
Failed to extract images from vg/lv
[root@bp-01 lvm2]# lvconvert -m -3 vg/lv /dev/sd[bc]1
Unable to remove 3 images: Only 2 devices given.
Failed to extract images from vg/lv
[root@bp-01 lvm2]# lvconvert -m -3 vg/lv /dev/sd[bcd]1
[root@bp-01 lvm2]# lvs -a -o name,attr,devices vg
LV Attr Devices
lv -wi-a----- /dev/sde1(1)
This patch doesn't work in all cases. The user can specify the right
number of devices, but not a sufficient amount of devices from the LV.
This will produce the old error message:
[root@bp-01 lvm2]# lvconvert -m -3 vg/lv /dev/sd[bcf]1
Unable to extract enough images to satisfy request
Failed to extract images from vg/lv
However, I think this error message is sufficient for this case.
Introduce a new parameter called "approx_alloc" that is set when the
desired size of a new LV is specified in percentage terms. If set,
the allocation code tries to get as much space as it can but does not
fail if can at least get some.
One of the practical implications is that users can now specify 100%FREE
when creating RAID LVs, like this:
~> lvcreate --type raid5 -i 2 -l 100%FREE -n lv vg
Optimize and cleanup recently introduced new function wipe_lv.
Use compound literals to get nicely initialized wipe_params struct.
Pass in lv as explicit argument for wipe_lv.
Use cmd from lv structure.
Initialize only non-null members so it's easy to see what
is the special arg.
Use common wipe_lv (former set_lv) fn to do zeroing as well as signature
wiping if needed. Provide new struct wipe_lv_params to define the
functionality.
Bind "lvcreate -W/--wipesignatures y" with proper wipe_lv call.
Also, add "yes" and "force" to lvcreate_params so it's possible
to apply them for the prompt: "WARNING: %s detected on %s. Wipe it? [y/n]".
Creation, deletion, [de]activation, repair, conversion, scrubbing
and changing operations are all now available for RAID LVs in a
cluster - provided that they are activated exclusively.
The code has been changed to ensure that no LV or sub-LV activation
is attempted cluster-wide. This includes the often overlooked
operations of activating metadata areas for the brief time it takes
to clear them. Additionally, some 'resume_lv' operations were
replaced with 'activate_lv_excl_local' when sub-LVs were promoted
to top-level LVs for removal, clearing or extraction. This was
necessary because it forces the appropriate renaming actions the
occur via resume in the single-machine case, but won't happen in
a cluster due to the necessity of acquiring a lock first.
The *raid* tests have been updated to allow testing in a cluster.
For the most part, this meant creating devices with '-aey' if they
were to be converted to RAID. (RAID requires the converting LV to
be EX because it is a condition of activation for the RAID LV in
a cluster.)
When images and their associated metadata are removed from a RAID1 LV,
the remaining sub-LVs are "shifted" down to fill the gaps. For
example, if there is a 3-way mirror:
[0][1][2]
and we remove device#0, the devices will be shifted down
[1][2]
and renamed.
[0][1]
This can create a problem for resume_lv (specifically,
dm_tree_activate_children) during the renaming process though. This
is because it will attempt to rename the higher indexed sub-LVs first
and find that it cannot because there are currently other sub-LVs with
that name. The solution is to check for a conflicting name before
attempting to rename. If a conflict is found and that conflicting
sub-LV is also in the process of renaming, we can defer the current
rename until the conflicting sub-LV has renamed and cleared the
conflict.
Now that resume_lv can handle these types of rename conflicts, we can
remove the workaround in RAID that was attempting to resume a RAID1
LV from the bottom-up in order to force a proper rename in assending
order before attempting a resume on the top-level LV. This "hack"
only worked for single machine use-cases of LVM. Clearing this up
paves the way for exclusive activation of RAID LVs in a cluster.
The function 'get_pv_list_for_lv' will assemble all the PVs that are
used by the specified LV. It uses 'for_each_sub_lv' to traverse all
of the sub-lvs which may compose it.
There are places where 'lv_is_active' was being used where it was
more correct to use 'lv_is_active_locally'. For example, when checking
for the existance of a kernel instance before asking for its status.
Most of the time these would work correctly. (RAID is only allowed on
non-clustered VGs at the moment, which means that 'lv_is_active' and
'lv_is_active_locally' would give the same result.) However, it is
more correct to use the proper variant and it helps with future
scenarios where targets might be allowed exclusively (or clustered) in
a cluster VG.
'lvchange' is used to alter a RAID 1 logical volume's write-mostly and
write-behind characteristics. The '--writemostly' parameter takes a
PV as an argument with an optional trailing character to specify whether
to set ('y'), unset ('n'), or toggle ('t') the value. If no trailing
character is given, it will set the flag.
Synopsis:
lvchange [--writemostly <PV>:{t|y|n}] [--writebehind <count>] vg/lv
Example:
lvchange --writemostly /dev/sdb1:y --writebehind 512 vg/raid1_lv
The last character in the 'lv_attr' field is used to show whether a device
has the WriteMostly flag set. It is signified with a 'w'. If the device
has failed, the 'p'artial flag has priority.
Example ("nosync" raid1 with mismatch_cnt and writemostly):
[~]# lvs -a --segment vg
LV VG Attr #Str Type SSize
raid1 vg Rwi---r-m 2 raid1 500.00m
[raid1_rimage_0] vg Iwi---r-- 1 linear 500.00m
[raid1_rimage_1] vg Iwi---r-w 1 linear 500.00m
[raid1_rmeta_0] vg ewi---r-- 1 linear 4.00m
[raid1_rmeta_1] vg ewi---r-- 1 linear 4.00m
Example (raid1 with mismatch_cnt, writemostly - but failed drive):
[~]# lvs -a --segment vg
LV VG Attr #Str Type SSize
raid1 vg rwi---r-p 2 raid1 500.00m
[raid1_rimage_0] vg Iwi---r-- 1 linear 500.00m
[raid1_rimage_1] vg Iwi---r-p 1 linear 500.00m
[raid1_rmeta_0] vg ewi---r-- 1 linear 4.00m
[raid1_rmeta_1] vg ewi---r-p 1 linear 4.00m
A new reportable field has been added for writebehind as well. If
write-behind has not been set or the LV is not RAID1, the field will
be blank.
Example (writebehind is set):
[~]# lvs -a -o name,attr,writebehind vg
LV Attr WBehind
lv rwi-a-r-- 512
[lv_rimage_0] iwi-aor-w
[lv_rimage_1] iwi-aor--
[lv_rmeta_0] ewi-aor--
[lv_rmeta_1] ewi-aor--
Example (writebehind is not set):
[~]# lvs -a -o name,attr,writebehind vg
LV Attr WBehind
lv rwi-a-r--
[lv_rimage_0] iwi-aor-w
[lv_rimage_1] iwi-aor--
[lv_rmeta_0] ewi-aor--
[lv_rmeta_1] ewi-aor--
When a device fails, we may wish to replace those segments with an
error segment. (Like when a 'vgreduce --removemissing' removes a
failed device that happens to be a RAID image/meta.) We are then left
with images that we will eventually want to remove or replace.
This patch allows us to pull out these virtual "error" sub-LVs. This
allows a user to 'lvconvert -m -1 vg/lv' to extract the bad sub-LVs.
Sub-LVs with error segments are considered for extraction before other
possible devices so that good devices are not accidentally removed.
This patch also adds the ability to replace RAID images that contain error
segments. The user will still be unable to run 'lvconvert --replace'
because there is no way to address the 'error' segment (i.e. no PV
that it is associated with). However, 'lvconvert --repair' can be
used to replace the image's error segment with a new PV. This is also
the most appropriate way to do it, since the LV will continue to be
reported as 'partial'.
