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The cache mode of a new cache pool is always explicitly
included in the vg metadata. If a cache mode is not
specified on the command line, the cache mode is taken
from lvm.conf allocation/cache_pool_cachemode, which
defaults to "writethrough".
The cache mode can be displayed with lvs -o+cachemode.
Currently, we have two modes of activation, an unnamed nominal mode
(which I will refer to as "complete") and "partial" mode. The
"complete" mode requires that a volume group be 'complete' - that
is, no missing PVs. If there are any missing PVs, no affected LVs
are allowed to activate - even RAID LVs which might be able to
tolerate a failure. The "partial" mode allows anything to be
activated (or at least attempted). If a non-redundant LV is
missing a portion of its addressable space due to a device failure,
it will be replaced with an error target. RAID LVs will either
activate or fail to activate depending on how badly their
redundancy is compromised.
This patch adds a third option, "degraded" mode. This mode can
be selected via the '--activationmode {complete|degraded|partial}'
option to lvchange/vgchange. It can also be set in lvm.conf.
The "degraded" activation mode allows RAID LVs with a sufficient
level of redundancy to activate (e.g. a RAID5 LV with one device
failure, a RAID6 with two device failures, or RAID1 with n-1
failures). RAID LVs with too many device failures are not allowed
to activate - nor are any non-redundant LVs that may have been
affected. This patch also makes the "degraded" mode the default
activation mode.
The degraded activation mode does not yet work in a cluster. A
new cluster lock flag (LCK_DEGRADED_MODE) will need to be created
to make that work. Currently, there is limited space for this
extra flag and I am looking for possible solutions. One possible
solution is to usurp LCK_CONVERT, as it is not used. When the
locking_type is 3, the degraded mode flag simply gets dropped and
the old ("complete") behavior is exhibited.
This avoids creating void matchers which have no effect anyway and
they just use resources. Also, it makes lvm dumpconfig --type diff
to mark these settings properly as not being different from defaults
(where by default, devices/preferred_names as well as devices/filter
are void).
Also, add a few comments about builtin rules used to select device
alias in case preferred_names is not defined or it doesn't match
any of device aliases.
The --binary option, if used, causes all the binary values reported
in reporting commands to be displayed as "0" or "1" instead of descriptive
literal values (value "unknown" is still used for values that could not be
determined).
Also, add report/binary_values_as_numeric lvm.conf option with the same
functionality as the --binary option (the --binary option prevails
if both --binary cmd option and report/binary_values_as_numeric lvm.conf
option is used at the same time). The report/binary_values_as_numeric is
also profilable.
This makes it easier to use and check lvm reporting command output in scripts.
The global/suffix was missing from example lvm.conf but it can
be very useful when using lvm in scripts and now in profiles as well
Let's expose it more.
man/lvm2-activation-generator.8:
Generator Specification -> Generators Specification
(this is the exact word in the systemd man page)
conf/example.conf.in:
cleanup recent edits related to report section
man/lvm.conf.5:
add a line about a possibility to generate a new
profile with lvm dumpconfig command as an alternative
to copying the default profile
Cache pools require a data and metadata area (like thin pools). Unlike
thin pool, if 'cache_pool_metadata_require_separate_pvs' is not set to
'1', the metadata and data area will be allocated from the same device.
It is also done in a manner similar to RAID, where a single chunk of
space is allocated and then split to form the metadata and data device -
ensuring that they are together.
When thin volume is using external origin, current thin target
is not able to supply 'extended' size with empty pages.
lvm2 detects version and disables extension of LV past the external
origin size in this case.
Thin LV could be however still reduced and extended freely bellow
this size.
There is a problem with the way mirrors have been designed to handle
failures that is resulting in stuck LVM processes and hung I/O. When
mirrors encounter a write failure, they block I/O and notify userspace
to reconfigure the mirror to remove failed devices. This process is
open to a couple races:
1) Any LVM process other than the one that is meant to deal with the
mirror failure can attempt to read the mirror, fail, and block other
LVM commands (including the repair command) from proceeding due to
holding a lock on the volume group.
2) If there are multiple mirrors that suffer a failure in the same
volume group, a repair can block while attempting to read the LVM
label from one mirror while trying to repair the other.
Mitigation of these races has been attempted by disallowing label reading
of mirrors that are either suspended or are indicated as blocking by
the kernel. While this has closed the window of opportunity for hitting
the above problems considerably, it hasn't closed it completely. This is
because it is still possible to start an LVM command, read the status of
the mirror as healthy, and then perform the read for the label at the
moment after a the failure is discovered by the kernel.
I can see two solutions to this problem:
1) Allow users to configure whether mirrors can be candidates for LVM
labels (i.e. whether PVs can be created on mirror LVs). If the user
chooses to allow label scanning of mirror LVs, it will be at the expense
of a possible hang in I/O or LVM processes.
2) Instrument a way to allow asynchronous label reading - allowing
blocked label reads to be ignored while continuing to process the LVM
command. This would action would allow LVM commands to continue even
though they would have otherwise blocked trying to read a mirror. They
can then release their lock and allow a repair command to commence. In
the event of #2 above, the repair command already in progress can continue
and repair the failed mirror.
This patch brings solution #1. If solution #2 is developed later on, the
configuration option created in #1 can be negated - allowing mirrors to
be scanned for labels by default once again.
Add allocation/thin_pool_chunk_size_calculation lvm.conf
option to select a method for calculating thin pool chunk
sizes and define two possible values - "default" and "performance".
lvmetad is not yet supported in clustered environment so
disable it automatically if using lvmconf --enable-cluster
and reset it to default value if using lvmconf --disable-cluster.
Also, add a few comments in lvm.conf about locking_type vs. use_lvmetad
if setting it for clustered environment.
When both the '-i' and '-m' arguments are specified on the command
line, use the "raid10" segment type. This way, the native RAID10
personality is used through dm-raid rather than layering a mirror
on striped LVs. If the old behavior is desired, the '--type'
argument to use would be "mirror" rather than "raid10".
Add new configure lvm.conf options for binaries thin_repair
and thin_dump.
Those are part of device-mapper-persistent-data package
and will be used for recovery of thin_pool.
The activation/auto_set_activation_skip enables/disables automatic
adding of the ACTIVATION_SKIP LV flag. By default thin snapshots
are flagged to be skipped during activation.
And by default, the auto_set_activation_skip is enabled.
