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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.
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!".
The problem as reported by "ben <benscott@nwlink.com>" on lvm-devel:
vgsplit fails with mirrored mirror log
#lvs --all -o lv_name,lv_attr,devices
LV Attr Devices
MyMirror mwi--
[MyMirror_mimage_0] Iwi--- /dev/sdq(0)
[MyMirror_mimage_1] Iwi--- /dev/sdo(0)
[MyMirror_mimage_2] Iwi--- /dev/sdi(0)
[MyMirror_mlog] mwi---
[MyMirror_mlog_mimage_0] Iwi--- /dev/sds(0)
[MyMirror_mlog_mimage_1] Iwi--- /dev/sde(0)
#vgsplit -v "TestA" "TestB" "/dev/sdq" "/dev/sdo" "/dev/sdi" "/dev/sds"
"/dev/sde"
Checking for volume group "TestA"
Checking for new volume group "TestB"
Archiving volume group "TestA" metadata (seqno 213).
Can't split mirror MyMirror between two Volume Groups
AFTER FIX:
[root@bp-01 ~]# lvs -a -o name,vg_name,devices vg new
Volume group "new" not found
Skipping volume group new
LV VG Devices
lv vg lv_mimage_0(0),lv_mimage_1(0)
[lv_mimage_0] vg /dev/sdb1(0)
[lv_mimage_1] vg /dev/sdc1(0)
[lv_mlog] vg lv_mlog_mimage_0(0),lv_mlog_mimage_1(0)
[lv_mlog_mimage_0] vg /dev/sdh1(0)
[lv_mlog_mimage_1] vg /dev/sdi1(0)
[root@bp-01 ~]# vgsplit vg new /dev/sd[bchi]1
New volume group "new" successfully split from "vg"
[root@bp-01 ~]# lvs -a -o name,vg_name,devices vg new
LV VG Devices
lv new lv_mimage_0(0),lv_mimage_1(0)
[lv_mimage_0] new /dev/sdb1(0)
[lv_mimage_1] new /dev/sdc1(0)
[lv_mlog] new lv_mlog_mimage_0(0),lv_mlog_mimage_1(0)
[lv_mlog_mimage_0] new /dev/sdh1(0)
[lv_mlog_mimage_1] new /dev/sdi1(0)
If you specify the segment type (e.g. --type mirror) and the mirrors argument
as zero, it would result in a mirrored LV with only one image. While the device
may be valid in theory, it should not be allowed in practice. It also makes it
difficult on the conversion tools, since they react badly to single-image
mirrors.
LVM has huge set of options now - it's approaching 60 short-arg less options
and we get interesting case of misdetection for 'merge' option which has been
put into the middle of options with 'short_arg' - thus certainly past 65. (ASCII 'A').
To avoid confusion of short_arg with long_opt number - add '128' to all such
non-short-arg options.
Makes dumpconfig whole-section output wrong in a different way from before,
but we should be able to merge cft_cmdline properly into cmd->cft now and
remove cascade.
leaving behind the LVM-specific parts of the code (convenience wrappers that
handle `struct device` and `struct cmd_context`, basically). A number of
functions have been renamed (in addition to getting a dm_ prefix) -- namely,
all of the config interface now has a dm_config_ prefix.
~> 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)
Move the free_vg() to vg.c and replace free_vg with release_vg
and make the _free_vg internal.
Patch is needed for sharing VG in vginfo cache so the release_vg function name
is a better fit here.
Defer the test of the function return value after the string memory is released.
Otherwise in this error path the string would present memory leak.
(Thought in this case we are already out of memory...)
Implementation described in doc/lvm2-raid.txt.
Basic support includes:
- ability to create RAID 1/4/5/6 arrays
- ability to delete RAID arrays
- ability to display RAID arrays
Notable missing features (not included in this patch):
- ability to clean-up/repair failures
- ability to convert RAID segment types
- ability to monitor RAID segment types
The conditional is not just unnecessary, it would have been wrong. The code
is suppose to be checking if the 'splitmirrors_ARG' is negative, but it
instead is checking 'mirrors_ARG'. Rather than changing the argument being
checked, I've pulled the check entirely because 'splitmirrors_ARG' is already
guarenteed to not be negative by virtue of the fact that it is a 'int_arg'.
Negative values will be caught in _process_command_line().
