IF YOU WOULD LIKE TO GET AN ACCOUNT, please write an
email to Administrator. User accounts are meant only to access repo
and report issues and/or generate pull requests.
This is a purpose-specific Git hosting for
BaseALT
projects. Thank you for your understanding!
Только зарегистрированные пользователи имеют доступ к сервису!
Для получения аккаунта, обратитесь к администратору.
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'.
Currently it is impossible to remove a failed PV which has a RAID LV
on it. This patch fixes the issue by replacing the failed PV with an
'error' segment within the affected sub-LVs. Once there is no longer
a RAID LV using the PV, it can be removed.
Most often, it is better to replace a failed RAID device with a spare.
(You can use 'lvconvert --repair <vg>/<LV>' to accomplish that.)
However, if there are no spares in the volume group and none will be
added, it is useful to be able to removed the failed device.
Following patches address the ability to perform 'lvconvert' operations
on RAID LVs that contain sub-LVs composed of 'error' segments.
We have been using 'mirror_region_size' in lvm.conf as the default region
size for RAID logical volumes as well as mirror logical volumes. Since,
"raid" is more inclusive and representative than "mirror", I have changed
the name of this setting. We must still check for the old setting and warn
the user if we are overriding it with the new setting if both happen to be
present.
If a RAID array is not in-sync, replacing devices should not be allowed
as a general rule. This is because the contents used to populate the
incoming device may be undefined because the devices being read where
not in-sync. The kernel enforces this rule unless overridden by not
allowing the creation of an array that is not in-sync and includes a
devices that needs to be rebuilt.
Since we cannot know the sync state of an LV if it is inactive, we must
also enforce the rule that an array must be active to replace devices.
That leaves us with the following conditions:
1) never allow replacement or repair of devices if the LV is in-active
2) never allow replacement if the LV is not in-sync
3) allow repair if the LV is not in-sync, but warn that contents may
not be recoverable.
In the case where a user is performing the repair on the command line via
'lvconvert --repair', the warning is printed before the user is prompted
if they would like to replace the device(s). If the repair is automated
(i.e. via dmeventd and policy is "allocate"), then the device is replaced
if possible and the warning is printed.
Use log_warn to print non-fatal warning messages.
Use of log_error would confuse checker for testing
whether proper error has been reported for some real error.
MD's bitmaps can handle 2^21 regions at most. The RAID code has always
used a region_size of 1024 sectors. That means the size of a RAID LV was
limited to 1TiB. (The user can adjust the region_size when creating a
RAID LV, which can affect the maximum size.) Thus, creating, extending or
converting to a RAID LV greater than 1TiB would result in a failure to
load the new device-mapper table.
Again, the size of the RAID LV is not limited by how much space is allocated
for the metadata area, but by the limitations of the MD bitmap. Therefore,
we must adjust the 'region_size' to ensure that the number of regions does
not exceed the limit. I've added code to do this when extending a RAID LV
(which covers 'create' and 'extend' operations) and when up-converting -
specifically from linear to RAID1.
Failing to clear the LV_NOTSYNCED flag when converting a RAID1 LV to
linear can result in the flag being present after an upconvert - even
if the sync is performed when upconverting.
Mirrors do not allow upconverting if the LV has been created with --nosync.
We will enforce the same rule for RAID1. It isn't hugely critical, since
the portions that have been written will be copied over to the new device
identically from either of the existing images. However, the unwritten
sections may be different, causing the added image to be a hybrid of the
existing images.
Also, we are disallowing the addition of new images to a RAID1 LV that has
not completed the initial sync. This may be different from mirroring, but
that is due to the fact that the 'mirror' segment type "stacks" when adding
a new image and RAID1 does not. RAID1 will rebuild a newly added image
"inline" from the existant images, so they should be in-sync.
We cannot add images to a RAID array while it is not in-sync. The
kernel will simply reject the table, saying:
'rebuild' specified while array is not in-sync
Now we check to ensure the LV is in-sync before attempting image
additions.
It is necessary when creating a RAID LV to clear the new metadata areas.
Failure to do so could result in a prepopulated bitmap that would cause
the new array to skip syncing portions of the array. It is a requirement
that the metadata LVs be activated and cleared in the process of creating.
However in test mode, this requirement should be lifted - no new LVs should
be created or written to.
When printing a message for the user and the lv_segment pointer is available,
use segtype->ops->name() instead of segtype->name. This gives a better
user-readable name for the segment. This is especially true for the
'striped' segment type, which prints "linear" if there is an area_count of
one.
Accept -q as the short form of --quiet.
Suppress non-essential standard output if -q is given twice.
Treat log/silent in lvm.conf as equivalent to -qq.
Review all log_print messages and change some to
log_print_unless_silent.
When silent, the following commands still produce output:
dumpconfig, lvdisplay, lvmdiskscan, lvs, pvck, pvdisplay,
pvs, version, vgcfgrestore -l, vgdisplay, vgs.
[Needs checking.]
Non-essential messages are shifted from log level 4 to log level 5
for syslog and lvm2_log_fn purposes.
This patch adds support for RAID10. It is not the default at this
stage. The user needs to specify '--type raid10' if they would like
RAID10 instead of stacked mirror over stripe.
If two devices in an array failed, it was previously impossible to replace
just one of them. This patch allows for the replacement of some, but perhaps
not all, failed devices.
The logic for resuming the original and newly split LVs was not properly
done to handle situations where anything but the last device in the array
was split. It did not take into account the possible name collisions that
might occur when the original LV undergoes the shifting and renaming of its
sub-LVs.
When down-converting a RAID1 device, it is the last device that is extracted
and removed when the user does not specify a particular device. However,
when a device is specified (and it is not the last), the device is removed and
the remaining sub-LVs are "shifted down" to fill the hole. This cause problems
when resuming the LV because if the shifted devices were resumed (and thus
renamed) before the sub-LV being extracted, there would be a name conflict.
The solution is to resume the extracted sub-LVs first so that they can be
properly renamed preventing a possible conflict.
This addresses bug 801967.
The code fail to account for the case where we just need a single device
in a RAID 4/5/6 array. There is no good way to tell the allocation functions
that we don't need parity devices when we are allocating just a single device.
So, I've used a bit of a hack. If we are allocating an area_count that is <=
the parity count, then we can assume we are simply allocating a replacement
device (i.e. no need to include parity devices in the calculations). This
should make sense in most cases. If we need to allocate replacement devices
due to failure (or moving), we will never allocate more than the parity count;
or we would cause the array to become unusable. If we are creating a new device,
we should always create more stripes than parity devices.
Failure to do so results in "Performing unsafe table load while X device(s) are
known to be suspended" errors. While fixing the problem in this way works and
is consistent with the way the mirror segment type does it, it would be nice
to find a solution that uses the generic suspend/resume calls.
Also included in this check-in are additions to the test suite that perform
conversions on RAID LVs under a snapshot. These tests are disabled for the
time being due to a kernel bug that is yet to be tracked down.
Also, don't allow a splitmirror operation on a RAID LV that is already tracking
a split, unless the operation is to stop the tracking and complete the split.
Example:
~> lvconvert --splitmirrors 1 --trackchanges vg/lv /dev/sdc1
# Now tracking changes - image can be merged back or split-off for good
~> lvconvert --splitmirrors 1 -n new_name vg/lv /dev/sdc1
# ^ Completes split ^
If a split is performed on a RAID that is tracking an already split image and
PVs are provided, we must ensure that
1) the already split LV is represented in the PVs
2) we are careful to split only the tracked image
RAID is not like traditional LVM mirroring. LVM mirroring required failed
devices to be removed or the logical volume would simply hang. RAID arrays can
keep on running with failed devices. In fact, for RAID types other than RAID1,
removing a device would mean substituting an error target or converting to a
lower level RAID (e.g. RAID6 -> RAID5, or RAID4/5 to RAID0). Therefore, rather
than removing a failed device unconditionally and potentially allocating a
replacement, RAID allows the user to "replace" a device with a new one. This
approach is a 1-step solution vs the current 2-step solution.
example> lvconvert --replace <dev_to_remove> vg/lv [possible_replacement_PVs]
'--replace' can be specified more than once.
example> lvconvert --replace /dev/sdb1 --replace /dev/sdc1 vg/lv
Example:
~> lvconvert --type raid1 vg/mirror_lv
Steps to convert "mirror" to "raid1"
1) Allocate a RAID metadata LV for each mirror image from the same PVs
on which they are located.
2) Clear the metadata LVs. This involves writing LVM metadata, so we don't
change any aspects of the mirror LV before this so that the user can easily
remove LVs from the failed convert attempt while retaining the original
mirror.
3) Remove the mirror log, if it exists.
4) Add metadata LVs to mirror LV
5) Rename mirror sub-lvs (s/mimage/rimage/)
6) Change flags and segtype from mirror to raid1
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.
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.
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.)
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.
This patch adds the ability to upconvert a raid1 array - say from 2-way to
3-way. It does not yet support upconverting linear to n-way.
The 'raid' device-mapper target allows for individual components (images) of
an array to be specified for rebuild. This mechanism is used when adding
new images to the array so that the new images can be resync'ed while the
rest of the images in the array can remain 'in-sync'. (There is no
mirror-on-mirror layering required.)
~> lvconvert --splitmirrors 1 --trackchanges vg/lv
The '--trackchanges' option allows a user the ability to use an image of
a RAID1 array for the purposes of temporary read-only access. The image
can be merged back into the array at a later time and only the blocks that
have changed in the array since the split will be resync'ed. This
operation can be thought of as a partial split. The image is never completely
extracted from the array, in that the array reserves the position the device
occupied and tracks the differences between the array and the split image via
a bitmap. The image itself is rendered read-only and the name (<LV>_rimage_*)
cannot be changed. The user can complete the split (permanently splitting the
image from the array) by re-issuing the 'lvconvert' command without the
'--trackchanges' argument and specifying the '--name' argument.
~> lvconvert --splitmirrors 1 --name my_split vg/lv
Merging the tracked image back into the array is done with the '--merge'
option (included in a follow-on patch).
~> lvconvert --merge vg/lv_rimage_<n>
The internal mechanics of this are relatively simple. The 'raid' device-
mapper target allows for the specification of an empty slot in an array
via '- -'. This is what will be used if a partial activation of an array
is ever required. (It would also be possible to use 'error' targets in
place of the '- -'.) If a RAID image is found to be both read-only and
visible, then it is considered separate from the array and '- -' is used
to hold it's position in the array. So, all that needs to be done to
temporarily split an image from the array /and/ cause the kernel target's
bitmap to track (aka "mark") changes made is to make the specified image
visible and read-only. To merge the device back into the array, the image
needs to be returned to the read/write state of the top-level LV and made
invisible.
Users already have the ability to split an image from an LV of "mirror"
segtype. This patch extends that ability to LVs of "raid1" segtype.
This patch only allows a single image to be split off, however. (The
"mirror" segtype allows an arbitrary number of images to be split off.
e.g. 4-way => 3-way/linear, 2-way/2-way, linear,3-way)
of top-level LV.
We can't activate sub-lv's that are being removed from a RAID1 LV while it
is suspended. However, this is what was being used to have them show-up
so we could remove them. 'sync_local_dev_names' is a sufficient and
proper replacement and can be done after the top-level LV is resumed.
1) add new function 'raid_remove_top_layer' which will be useful
to other conversion functions later (also cleans up code)
2) Add error messages if raid_[extract|add]_images fails
3) Add function prototypes to prevent compiler warnings when
compiling with '--with-raid=shared'
Fix a couple more issues that kabi found.
- Add some error messages in failure cases
- s/malloc/zalloc/
- use vg->vgmem for lv names instead of vg->cmd->mem
