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If a single, standard LV is specified as the cache, use
it directly instead of converting it into a cache-pool
object with two separate LVs (for data and metadata).
With a single LV as the cache, lvm will use blocks at the
beginning for metadata, and the rest for data. Separate
dm linear devices are set up to point at the metadata and
data areas of the LV. These dm devs are given to the
dm-cache target to use.
The single LV cache cannot be resized without recreating it.
If the --poolmetadata option is used to specify an LV for
metadata, then a cache pool will be created (with separate
LVs for data and metadata.)
Usage:
$ lvcreate -n main -L 128M vg /dev/loop0
$ lvcreate -n fast -L 64M vg /dev/loop1
$ lvs -a vg
LV VG Attr LSize Type Devices
main vg -wi-a----- 128.00m linear /dev/loop0(0)
fast vg -wi-a----- 64.00m linear /dev/loop1(0)
$ lvconvert --type cache --cachepool fast vg/main
$ lvs -a vg
LV VG Attr LSize Origin Pool Type Devices
[fast] vg Cwi---C--- 64.00m linear /dev/loop1(0)
main vg Cwi---C--- 128.00m [main_corig] [fast] cache main_corig(0)
[main_corig] vg owi---C--- 128.00m linear /dev/loop0(0)
$ lvchange -ay vg/main
$ dmsetup ls
vg-fast_cdata (253:4)
vg-fast_cmeta (253:5)
vg-main_corig (253:6)
vg-main (253:24)
vg-fast (253:3)
$ dmsetup table
vg-fast_cdata: 0 98304 linear 253:3 32768
vg-fast_cmeta: 0 32768 linear 253:3 0
vg-main_corig: 0 262144 linear 7:0 2048
vg-main: 0 262144 cache 253:5 253:4 253:6 128 2 metadata2 writethrough mq 0
vg-fast: 0 131072 linear 7:1 2048
$ lvchange -an vg/min
$ lvconvert --splitcache vg/main
$ lvs -a vg
LV VG Attr LSize Type Devices
fast vg -wi------- 64.00m linear /dev/loop1(0)
main vg -wi------- 128.00m linear /dev/loop0(0)
As we start refactoring the code to break dependencies (see doc/refactoring.txt),
I want us to use full paths in the includes (eg, #include "base/data-struct/list.h").
This makes it more obvious when we're breaking abstraction boundaries, eg, including a file in
metadata/ from base/
'lvdisplay -m' tried to go through NULL policy settings,
when such policy was not defined for CachedLV.
Patch is fixing display of cache-pool without defined settings,
as this is now a valid pool and we mostly want users to define
these settings when actually really caching a LV.
With monolithic kernels we can't actually modprobe
for cache modules as they are already compiled-in
and policy modules do not export version symbol.
Reported issue on list:
https://www.redhat.com/archives/dm-devel/2017-March/msg00061.html
Fix will try to look for explicit kernel symbols first before
calling modprobe.
Better support for lvdisplay.
By default info about running (in kernel) cache status is printed.
To get 'segtype' info, user runs: 'lvdisplay -m', example:
--- Logical volume ---
LV Path /dev/vg/lvol0
LV Name lvol0
VG Name vg
LV UUID Y4uWuN-TBGk-duer-aPWl-yBWn-iFFR-RU1gg1
LV Write Access read/write
LV Creation host, time linux, 2017-03-01 20:52:39 +0100
LV Cache pool name lvol2
LV Cache origin name lvol0_corig
LV Status available
# open 0
LV Size 12,00 MiB
Cache used blocks 10,42%
Cache metadata blocks 0,49%
Cache dirty blocks 0,00%
Cache read hits/misses 112 / 34
Cache wrt hits/misses 133 / 0
Cache demotions 0
Cache promotions 20
Current LE 3
Segments 1
Allocation inherit
Read ahead sectors auto
- currently set to 256
Block device 253:0
--- Segments ---
Logical extents 0 to 2:
Type cache
Chunk size 64,00 KiB
Metadata format 1
Mode writethrough
Policy smq
Setting migration_threshold=100000
Cache pool read/writes metadata_format within its segment type..
For CachePoolLV unselected metadata format is NOT stored in metadata.
For CacheLV when metadata format is not present/selected in lvm2 metadata,
it's automatically assumed to be the version 1 (backward compatible).
To ensure older lvm2 will not 'miss-read' metadata with new version 2,
such LV is marked with METADATA_FORMAT status flag (segment is
specifying metadata format). So when cache uses metadata format 2,
it will become inaccesible on older system without such support.
(kernel dm cache < 1.10, lvm2 < 2.02.169).
Add new profilable configation setting to let user select
which metadata format of a created cache pool he wish to use.
By default the 'best' available format is autodetected at runtime,
but user may enforce format 1 or 2 ATM.
Code also detects availability for metadata2 supporting cache target.
In case of troubles user may easily Disable usage of this feature
by placing 'metadata2' into global/cache_disabled_features list.
Add support for active cache LV.
Handle --cachemode args validation during command line processing.
Rework some lvm2 internal to use lvm2 defined CACHE_MODE enums
indepently on libdm defines and use enum around the code instead
of passing and comparing strings.
Add support for making an interconnection between thin LV segment and
its indirect origin (which may be historical or live LV) - add a new
"indirect_origin" argument to attach_pool_lv function.
When reading older lvm2 metadata for cache-pool - we now handle more
extended syntax - basically we want to enter most setting when
actually creating cached LV.
For this new validation code has been added. However older metadata
without new settings set is now found as invalid.
Fix it by adding default settings for cache policy mq
and cache mode writethrough.
Change logic and naming of some internal API functions.
cache_set_mode() and cache_set_policy() both take segment.
cache mode is now correctly 'masked-in'.
If the passed segment is 'cache' segment - it will automatically
try to find 'defaults' according to profiles if the are NOT
specified on command line or they are NOT already set for cache-pool.
These defaults are never set for cache-pool.
Add code to detect available cache features.
Support policy_mq & policy_smq features which might be disabled.
Introduce global_cache_disabled_features_CFG.
Add new profilable configurables:
allocation/cache_policy
allocation/cache_settings
and mark allocation/cache_pool_chunk_size as profilable as well.
Obsolete allocation/cache_pool_cachemode and
introduce new allocation/cache_mode instead.
Rename DEFAULT_CACHE_POOL_POLICY to DEFAULT_CACHE_POLICY.
Policy name has to be always defined.
Capture it as an internal error before write.
When reading metadata without defined policy name, use default defined policy.
TODO: Unsure, but it might have to be actually always 'mq' in this case.
When cache_mode is undefined, the read of metadata will miss to
set a bit with mode and fails to process metadata on internal
error:
Internal error: LV vg/lvol1 has uknown feature flags 0.
Fix it by setting it to writethrough mode.
Do not use 'any' policy name as a value in config tree - so we stick
with 'policy_settings' and extra 'policy_name' for libdm params.
Update lvm2 API as well.
Example of supported metadata:
policy = "mq"
policy_settings {
migration_threshold = 2048
sequential_threshold = 512
random_threshold = 4
read_promote_adjustment = 10
}
Support new PASSTHROUGH 'feature' flag.
Add dm_config_node to pass in policy args.
Really use origin_uuid instead of using extra call
to pass seg_areas.
Switch to 64bit feature flag bit set so there is
enough space in future for new bits...
Use segment flags to avoid zeroing of cache, cache pool
snapshot and thin pool segments.
We never want to zero these segment types.
Note:
Snapshot COW and Cache origin are created as stripes
thus are then properly zeroed.
