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To avoid polution of metadata with some 'garbage' content or eventualy
some leak of stale data in case user want to upload metadata somewhere,
ensure upon allocation the metadata device is fully zeroed.
Behaviour may slow down allocation of thin-pool or cache-pool a bit
so the old behaviour can be restored with lvm.conf setting:
allocation/zero_metadata=0
TODO: add zeroing for extension of metadata volume.
Failure in wiping/zeroing stop the command.
If user wants to avoid command abortion he should use -Zn or -Wn
to avoid wiping.
Note: there is no easy way to distinguish which kind of failure has
happend - so it's safe to not proceed any futher.
When initiated larger write request, it may have happened, bcache
got out of free chunks - fix the loop, that is supposed to wait
until next free chunk becomes avain available.
To create a new cache or writecache LV with a single command:
lvcreate --type cache|writecache
-n Name -L Size --cachedevice PVfast VG [PVslow ...]
- A new main linear|striped LV is created as usual, using the
specified -n Name and -L Size, and using the optionally
specified PVslow devices.
- Then, a new cachevol LV is created internally, using PVfast
specified by the cachedevice option.
- Then, the cachevol is attached to the main LV, converting the
main LV to type cache|writecache.
Include --cachesize Size to specify the size of cache|writecache
to create from the specified --cachedevice PVs, otherwise the
entire cachedevice PV is used. The --cachedevice option can be
repeated to create the cache from multiple devices, or the
cachedevice option can contain a tag name specifying a set of PVs
to allocate the cache from.
To create a new cache or writecache LV with a single command
using an existing cachevol LV:
lvcreate --type cache|writecache
-n Name -L Size --cachevol LVfast VG [PVslow ...]
- A new main linear|striped LV is created as usual, using the
specified -n Name and -L Size, and using the optionally
specified PVslow devices.
- Then, the cachevol LVfast is attached to the main LV, converting
the main LV to type cache|writecache.
In cases where more advanced types (for the main LV or cachevol LV)
are needed, they should be created independently and then combined
with lvconvert.
Example
-------
user creates a new VG with one slow device and one fast device:
$ vgcreate vg /dev/slow1 /dev/fast1
user creates a new 8G main LV on /dev/slow1 that uses all of
/dev/fast1 as a writecache:
$ lvcreate --type writecache --cachedevice /dev/fast1
-n main -L 8G vg /dev/slow1
Example
-------
user creates a new VG with two slow devs and two fast devs:
$ vgcreate vg /dev/slow1 /dev/slow2 /dev/fast1 /dev/fast2
user creates a new 8G main LV on /dev/slow1 and /dev/slow2
that uses all of /dev/fast1 and /dev/fast2 as a writecache:
$ lvcreate --type writecache --cachedevice /dev/fast1 --cachedevice /dev/fast2
-n main -L 8G vg /dev/slow1 /dev/slow2
Example
-------
A user has several slow devices and several fast devices in their VG,
the slow devs have tag @slow, the fast devs have tag @fast.
user creates a new 8G main LV on the slow devs with a
2G writecache on the fast devs:
$ lvcreate --type writecache -n main -L 8G
--cachedevice @fast --cachesize 2G vg @slow
To add a cache or writecache to a main LV with a single command:
lvconvert --type cache|writecache --cachedevice /dev/ssd vg/main
A cachevol LV will be allocated from the specified cache device,
then attached to the main LV. Include --cachesize to specify the
size of cachevol to create, otherwise the entire cachedevice is
used. The cachedevice option can be repeated to create a cachevol
from multiple devices.
Example
-------
A user has an existing main LV that they want to speed up
using a new ssd.
user adds the new ssd to the VG:
$ vgextend vg /dev/ssd
user attaches the new ssd their main LV:
$ lvconvert --type writecache --cachedevice /dev/ssd vg/main
Example
-------
A user has two existing main LVs that they want to speed up
with a new ssd.
user adds the new 16G ssd to the VG:
$ vgextend vg /dev/ssd
user attaches some of the new ssd to the first main LV,
using half of the space:
$ lvconvert --type writecache --cachedevice /dev/ssd
--cachesize 8G vg/main1
user attaches some of the new ssd to the second main LV,
using the other half of the space:
$ lvconvert --type writecache --cachedevice /dev/ssd
--cachesize 8G vg/main2
Example
-------
A user has an existing main LV that they want to speed up using
two new ssds.
user adds the new two ssds the VG:
$ vgextend vg /dev/ssd1
$ vgextend vg /dev/ssd2
user attaches both ssds their main LV:
$ lvconvert --type writecache
--cachedevice /dev/ssd1 --cachedevice /dev/ssd2 vg/main
Use libblkid to detect sector/block size of the fs on the LV.
Use this to choose a compatible writecache block size.
Enable attaching writecache to an active LV.
When lvconvert is used to remove raid images, we can
skip calling lv_add_integrity_to_raid(), which finds
nothing to do, but the the blocksize validation would
be called unnecessarily and trigger spurious errors.
The test was using a raid+integrity LV without
first waiting for the integrity sync, which could
cause the test to fail (depending on init speed)
where it depends on integrity to work in uninitialized
areas.
Also use cmp instead of diff.
pvck --dump headers reads the metadata text area
to compute the text metadata checksum to compare
with the mda_header checksum.
The new header_only will skip reading the metadata
text and not validate the mda_header checksum.
