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Add basic support for converting LV into an external origin volume.
Syntax:
lvconvert --thinpool vg/pool --originname renamed_origin -T origin
It will convert volume 'origin' into a thin volume, which will
use 'renamed_origin' as an external read-only origin.
All read/write into origin will go via 'pool'.
renamed_origin volume is read-only volume, that could be activated
only in read-only mode, and cannot be modified.
Support swapping of metadata device if the thin pool already
exists. This way it's easy to i.e. resize metadata or their
repair operation.
User may create some empty LV, replace existing metadata
or dump and restore them into bigger LV.
Update code for lvconvert.
Change the lvconvert user interface a bit - now we require 2 specifiers
--thinpool takes LV name for data device (and makes the name)
--poolmetadata takes LV name for metadata device.
Fix type in thin help text -z -> -Z.
Supported is also new flag --discards for thinpools.
Support has many limitations and lots of FIXMEs inside,
however it makes initial task when user creates a separate LV for
thin pool data and thin metadata already usable, so let's enable
it for testing.
Easiest API:
lvconvert --chunksize XX --thinpool data_lv metadata_lv
More functionality extensions will follow up.
TODO: Code needs some rework since a lot of same code is getting copied.
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
~> 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.
page.
Add ->target_name to segtype_handler to allow a more specific target
name to be returned based on the state of the segment.
Result of trying to merge a snapshot using a kernel that doesn't have
the snapshot-merge target:
Before:
# lvconvert --merge vg/snap
Can't expand LV lv: snapshot target support missing from kernel?
Failed to suspend origin lv
After:
# lvconvert --merge vg/snap
Can't process LV lv: snapshot-merge target support missing from kernel?
Failed to suspend origin lv
Unable to merge LV "snap" into it's origin.
{core|disk|mirrored}. However, under the options section they are
described as {core|disk} - even though the 'mirrored' argument is
described.
s/'{core|disk}'/'{core|disk|mirrored}'/
This check-in enables the 'mirrored' log type. It can be specified
by using the '--mirrorlog' option as follows:
#> lvcreate -m1 --mirrorlog mirrored -L 5G -n lv vg
I've also included a couple updates to the testsuite. These updates
include tests for the new log type, and some fixes to some of the
*lvconvert* tests.
Switch lvconvert's --merge code over to using process_each_lv(). Doing
so adds support for a single 'lvconvert --merge' to start merging
multiple LVs (which includes @tag expansion).
Add 'lvconvert --merge @tag' testing to test/t-snapshot-merge.sh
Adjust man/lvconvert.8.in to reflect these expanded capabilities.
The lvconvert.c implementation requires rereading the VG each iteration
of process_each_lv(). Otherwise a stale VG instance associated with
the LV passed to lvconvert_single_merge() would result in stale VG
metadata being written back out to disk. This overwrote new metadata
that was written when a previous snapshot LV finished merging (via
lvconvert_poll). This is only an issue when merging multiple LVs that
share the same VG (a single VG is typical for most LVM configurations on
system disks).
In the end this new support is very useful for performing a "system
rollback" that requires multiple snapshot LVs be merged to their
respective origin LV.
The yum-utils 'fs-snapshot' plugin tags all snapshot LVs that it creates
with a common 'snapshot_tag' that is unique to the yum transaction.
Rolling back a yum transaction, that created LVM snapshots with the tag
'yum_20100129133223', is as simple as:
lvconvert --merge @yum_20100129133223
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
