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Since lvm does support external users of thin-pool when thin devices
are managed outside it can be useful to support conversion to
thin pool from data and metadata LV without zeroing.
TransactionID will be 0 in lvm2 metadata.
lvconvert -Zn --thinpool vg/data --poolmetadata vg/meta
Renables usage of --type zero and --type error LVs to serve as
backend for _tdata device. Clearly not very useful in practice,
as it can't store any real data, but usable for some testing
and some sort of perfomance checking.
lvcreate --type zero -L1T -n pool vg
lvconvert --thinpool vg/pool
Will create a thin-pool with zero device backend.
Enabled extension/mixing of stripes/linears, error and zero
segtype LVs with stripes/linear, error and zero segtypes.
It is not very useful in practice, as the user cannot store any real
data on error or zero segtypes, but it may get some uses in
some scenarios where i.e. some portion of the device should not be
readable. Mixing of types happens on 'extent_size' level:
lvcreate -L1 -n lv vg
lvextend --type error -L+1 vg/lv
lvextend --type zero -L+1 vg/lv
lvextend --type linear -L+1 vg/lv
lvextend --type striped -L+1 vg/lv
lvs -o+segtype,seg_size vg
Note: when the type is not specified, the last segment type is
automatically selected.
It's also a small 'can of worms' since we can't tell LVs if
the LV is linear/error/zero or their mixtures. So the meaning behind
them may need some updates.
We already have this types of LV created i.e by:
vgreduce --removemissing --force
where missing LV segments have been replaced by either
error or zero segtype (lvm.conf).
TODO: it might be worth adding a message while such device is activated.
When multiple polling tasks are watching for same LV, clearly
when some of them wins the game - other polling tasks will fail.
Improve the logic and report success if the merged LV is
actually not a merging origin anymore (since likely someone
else has already finished merging).
Although we support '0' interval - it's highly inefficent to
do so many scans in busy-loop.
So ATM raise minimal rescan time to 100ms.
TODO: revisit whole timing logic here as it does have some sideeffect
hiddent impact and can considerably eat CPU in some cases.
There is really no practical reason to continue running
when we fail on allocation.
It seems we may need further fine frained errors, as for
some error type we simply need to exit ASAP, while
others may still produce usable results.
When generating list of processed LV, add thin-pool to the head of the
list, while other LVs are added on tail.
This makes it easier when removing many thin volumes, to recognize easily
when its thin-pool is also supposed to be removed.
The correct test needs to actually check 'lv->snapshot' is not NULL,
so the 'find_snapshot()' can work.
Test lv_is_snapshot was actually irrelavant for this case.
Also initialize device_id.
This patch postpones update of lvm metadata for each removed
LV for later moment depending on LV type.
It also queues messages to be printed after such write & commit.
As such there is some change in the behavior - although before
prompt we do make write&commit happens automatically in some
other error case we rather keep 'existing' state - so there
could be difference in amount of removed & commited LVs.
IMHO introduce logic is slightly better and more save.
But some cases still need the early commit - i.e. thin-removal
and fixing this needs some more thinking.
TODO: improve removal at least with the case of the whole thin-pool.
i.e. we can simply recognize removal of 'all LVs/whole VG'.
Taking backup with each removed LV is slowing down the process
considerable and is largerly uneeded. We are supposed to take
backup only on significant points and making sure the backup
is correct when the command is finished.
TODO: check how many other commands can be improved.
The LVM devices file lists devices that lvm can use. The default
file is /etc/lvm/devices/system.devices, and the lvmdevices(8)
command is used to add or remove device entries. If the file
does not exist, or if lvm.conf includes use_devicesfile=0, then
lvm will not use a devices file. When the devices file is in use,
the regex filter is not used, and the filter settings in lvm.conf
or on the command line are ignored.
LVM records devices in the devices file using hardware-specific
IDs, such as the WWID, and attempts to use subsystem-specific
IDs for virtual device types. These device IDs are also written
in the VG metadata. When no hardware or virtual ID is available,
lvm falls back using the unstable device name as the device ID.
When devnames are used, lvm performs extra scanning to find
devices if their devname changes, e.g. after reboot.
When proper device IDs are used, an lvm command will not look
at devices outside the devices file, but when devnames are used
as a fallback, lvm will scan devices outside the devices file
to locate PVs on renamed devices. A config setting
search_for_devnames can be used to control the scanning for
renamed devname entries.
Related to the devices file, the new command option
--devices <devnames> allows a list of devices to be specified for
the command to use, overriding the devices file. The listed
devices act as a sort of devices file in terms of limiting which
devices lvm will see and use. Devices that are not listed will
appear to be missing to the lvm command.
Multiple devices files can be kept in /etc/lvm/devices, which
allows lvm to be used with different sets of devices, e.g.
system devices do not need to be exposed to a specific application,
and the application can use lvm on its own set of devices that are
not exposed to the system. The option --devicesfile <filename> is
used to select the devices file to use with the command. Without
the option set, the default system devices file is used.
Setting --devicesfile "" causes lvm to not use a devices file.
An existing, empty devices file means lvm will see no devices.
The new command vgimportdevices adds PVs from a VG to the devices
file and updates the VG metadata to include the device IDs.
vgimportdevices -a will import all VGs into the system devices file.
LVM commands run by dmeventd not use a devices file by default,
and will look at all devices on the system. A devices file can
be created for dmeventd (/etc/lvm/devices/dmeventd.devices) If
this file exists, lvm commands run by dmeventd will use it.
Internal implementaion:
- device_ids_read - read the devices file
. add struct dev_use (du) to cmd->use_devices for each devices file entry
- dev_cache_scan - get /dev entries
. add struct device (dev) to dev_cache for each device on the system
- device_ids_match - match devices file entries to /dev entries
. match each du on cmd->use_devices to a dev in dev_cache, using device ID
. on match, set du->dev, dev->id, dev->flags MATCHED_USE_ID
- label_scan - read lvm headers and metadata from devices
. filters are applied, those that do not need data from the device
. filter-deviceid skips devs without MATCHED_USE_ID, i.e.
skips /dev entries that are not listed in the devices file
. read lvm label from dev
. filters are applied, those that use data from the device
. read lvm metadata from dev
. add info/vginfo structs for PVs/VGs (info is "lvmcache")
- device_ids_find_renamed_devs - handle devices with unstable devname ID
where devname changed
. this step only needed when devs do not have proper device IDs,
and their dev names change, e.g. after reboot sdb becomes sdc.
. detect incorrect match because PVID in the devices file entry
does not match the PVID found when the device was read above
. undo incorrect match between du and dev above
. search system devices for new location of PVID
. update devices file with new devnames for PVIDs on renamed devices
. label_scan the renamed devs
- continue with command processing
User use 'lvconvert -Zn --type vdo-pool' to convert an existing
vdo formated volume and skip lvm2 internal formating.
This however requires user is passing proper matching parameters.
For them user can use --profile|--metadataprofile option whos
support has been also enhanced.
TODO: add support to read values directly from formated volume.
