Driver `sync.btrfs`

Minimal configlet:

[sync#1]
type = btrfs
src = {fs#1.label}:{fs#1.subvol}
target =

Minimal setup command:

om test/vol/foo set \
	--kw="type=btrfs" \
	--kw="src={fs#1.label}:{fs#1.subvol}" \
	--kw="target="

Supported keywords:

blocking_post_provision
blocking_post_unprovision
blocking_pre_provision
blocking_pre_unprovision
comment
disable
dst
encap
log
max_delay
max_lag_age
monitor
optional
pg_blkio_weight
pg_cpu_burst
pg_cpu_quota
pg_cpu_shares
pg_cpus
pg_mem_high
pg_mem_limit
pg_mem_oom_control
pg_mem_swappiness
pg_mems
pg_pids_max
pg_vmem_limit
post_provision
post_unprovision
pre_provision
pre_unprovision
provision
provision_requires
recursive
schedule
shared
src
standby
stat_timeout
subset
tags
target
timeout
type
unprovision
unprovision_requires
update_requires

Keyword `blocking_post_provision`

required:    false
scopable:    true
rbac:        Triggers require the root grant.

Description:

A command or script to execute after the resource provision action.

Errors interrupt the action.

This trigger is only executed on leaders.

Keyword `blocking_post_unprovision`

required:    false
scopable:    true
rbac:        Triggers require the root grant.

Description:

A command or script to execute after the resource unprovision action.

Errors interrupt the action.

This trigger is only executed on leaders.

Keyword `blocking_pre_provision`

required:    false
scopable:    true
rbac:        Triggers require the root grant.

Description:

A command or script to execute before the resource provision action.

Errors interrupt the action.

Keyword `blocking_pre_unprovision`

required:    false
scopable:    true
rbac:        Triggers require the root grant.

Description:

A command or script to execute before the resource unprovision action.

Errors interrupt the action.

Keyword `comment`

required:    false
scopable:    false

Description:

A free form text describing the role of the object, of the node, or of the section it is set in.

The keyword is accepted in any section, so the DEFAULT section can document a configuration as a whole, and a resource, pool, heartbeat, array or network section can document itself.

The agent does not interpret the value.

Keyword `disable`

required:    false
scopable:    true
convert:     bool

Description:

A disabled resource will be ignored on start, stop, provision and unprovision actions.

A disabled resource status is n/a.

If set in the DEFAULT section of an object, the object is disabled and ignores start, stop, shutdown, provision and unprovision actions.

These actions immediately return success.

om <path> disable sets DEFAULT.disable=true.

om <path> enable sets DEFAULT.disable=false.

Note: The enable and disable actions preserve the individual resource disable state.

Keyword `dst`

required:    false
scopable:    true
rbac:        Requires the root grant.

Example:

dst=svc1fs:data

Description:

Destination subvolume of the sync, as <label>:<subvol>. It defaults to src.

On a peer, the destination subvolume is replaced by a writable snapshot of the last copy received, at every sync. A peer with its destination subvolume mounted, which is a peer running the service, is refused: its data would be replaced.

Keyword `encap`

required:    false
scopable:    false
convert:     bool

Description:

Set to true to ignore this resource in the nodes context and consider it in the encapnodes context. The resource is thus handled by agents deployed in the service containers.

Keyword `log`

required:    false
scopable:    true
default:     false
convert:     bool
rbac:        A keyword of the btrfs driver, which needs the root grant to choose.

Description:

Log the scheduled runs of the resource, the updates the daemon scheduler starts, as a run asked by a user is.

The daemon scheduler logs the runs of the jobs it starts only when they ask it, so a scheduled update of a resource with log = false leaves no trace in the journal but its status.

Keyword `max_delay`

required:    false
scopable:    false
aliases:     sync_max_delay
convert:     duration
rbac:        A keyword of the btrfs driver, which needs the root grant to choose.

Description:

The delay above which the status of the resource reports warn.

It should be set according to your application service level agreement.

The scheduler task interval should be lower than max_delay.

Keyword `max_lag_age`

required:    false
scopable:    true
default:     24h
convert:     duration
rbac:        Requires the root grant.

Example:

max_lag_age=3d

Description:

How long a peer may miss the updates before the source stops keeping its base snapshot.

A peer that missed updates is sent the changes since the last snapshot it received, which the source keeps for it. The first update the peer misses starts its lag. Once the lag exceeds this duration, the source deletes that snapshot and stops sending to the peer. From then on the peer needs a full copy, asked with om <path> instance full --rid <rid> --target <peer>, and the resource status warns until then.

Keyword `monitor`

required:    false
scopable:    true
convert:     bool

Description:

A resource with monitor=true will trigger the monitor_action (crash or reboot the node, freezestop or switch the service) if:

The resource is down.
The instance has local_expect=started in its daemon monitor data, which means the daemon considers this instance is and should remain started.
All restart tentatives failed.

Keyword `optional`

required:    false
scopable:    true
convert:     bool

Description:

Action errors on optional resources are logged but do not interrupt the action sequence.

The status of optional resources is not included in the instance availability status but is considered in the overall status.

The status of task and sync resources is always included in the overall status, regardless of whether they are marked as optional.

Resources tagged as noaction are considered optional by default.

Dump filesystems are a typical use case for optional=true.

Keyword `pg_blkio_weight`

required:    false
scopable:    true

Example:

pg_blkio_weight=50

Description:

Block IO relative weight. Value: between 10 and 1000.

The kernel default is 100.

Setting this keyword to default puts the capping back where a node that never capped anything leaves it. Removing the keyword does not: what was written stays written, whether om wrote it or something else did.

Keyword `pg_cpu_burst`

required:    false
scopable:    true

Example:

pg_cpu_burst=20%

Description:

The cpu time the group banks under its quota, and spends above it.

It is the time the processes of the group may bank while under their pg_cpu_quota, and spend above it in a short spike, in the notation of pg_cpu_quota: 20% lets the group run a fifth of a cpu above its quota during a period, out of what it left unused before.

It serves a latency-sensitive service capped tightly: a request arriving after an idle spell is served at the speed of the burst, rather than throttled for the rest of the period. Over a longer time the group still uses no more than its quota.

It needs pg_cpu_quota, and cannot exceed it: the kernel refuses a burst larger than the quota. Only the unified cgroup hierarchy has it.

Keyword `pg_cpu_quota`

required:    false
scopable:    true

Example:

pg_cpu_quota=50%@all

Description:

The percentage of cpu time the processes of the group may use.

Accepted expressions:

50% Half of one cpu.
50%@all Half of every cpu the node has.
10%@2 A tenth of two cpus.

Unlike pg_cpu_shares, which only arbitrates when the node is cpu-bound, a quota caps the group whether or not the node is busy.

Keyword `pg_cpu_shares`

required:    false
scopable:    true
convert:     size

Example:

pg_cpu_shares=512

Description:

The share of cpu the group gets when the node is cpu-bound.

The share is relative to the other groups.

The actual percentile depends on the shares allowed to the other services. Unset, the kernel default is used, which usually is 1024 shares.

Keyword `pg_cpus`

required:    false
scopable:    true
depends:     create_pg=true

Example:

pg_cpus=0-2

Description:

The cpus the processes of the group may run on.

Cpus are specified as list or range : 0,1,2 or 0-2.

Keyword `pg_mem_high`

required:    false
scopable:    true
convert:     size

Example:

pg_mem_high=384m

Description:

The memory past which the kernel throttles the group, in bytes.

Past it, the kernel slows the processes of the group down, reclaiming their memory and throttling their allocations.

Unlike pg_mem_limit, reaching it does not wake the Out-Of-Memory killer: a group above it keeps running, slower, while the kernel reclaims. Set below pg_mem_limit, it gives a process growing too much the time to be noticed, or to shrink, before it is killed.

It is a soft limit, so it is not what a memory claim counts: the claim counts pg_mem_limit. Only the unified cgroup hierarchy has it.

Keyword `pg_mem_limit`

required:    false
scopable:    true
convert:     size

Example:

pg_mem_limit=512m

Description:

The memory the processes of the group may use, in bytes.

The Out-Of-Memory killer is triggered in case of tresspassing.

Keyword `pg_mem_oom_control`

required:    false
scopable:    true

Example:

pg_mem_oom_control=1

Description:

Whether the Out of Memory killer runs for the group: 0 enables it.

It is a flag (0 or 1) enabling or disabling the Out of Memory killer for the processes of the group.

If enabled (0), tasks that attempt to consume more memory than they are allowed are immediately killed by the OOM killer.
If disabled (1), tasks are allowed to continue to try allocating memory, stressing the system.

The OOM killer is enabled by default in every cgroup using the memory controller.

This keyword caps nothing on a node holding the unified cgroup hierarchy, which has no memory.oom_control: that file is of the v1 hierarchy. Setting it there is warned about, and ignored.

Keyword `pg_mem_swappiness`

required:    false
scopable:    true

Example:

pg_mem_swappiness=40

Description:

Set a swappiness percentile value for the process group.

This keyword caps nothing on a node holding the unified cgroup hierarchy, which has no memory.swappiness: that file is of the v1 hierarchy. Setting it there is warned about, and ignored.

Keyword `pg_mems`

required:    false
scopable:    true

Example:

pg_mems=0-2

Description:

The memory nodes the processes of the group may allocate from.

Memory nodes are specified as list or range : 0,1,2 or 0-2.

Keyword `pg_pids_max`

required:    false
scopable:    true

Example:

pg_pids_max=512

Description:

The most processes and threads the group may run at once.

A fork beyond it fails in the process that asked for it, and nothing else of the node is touched: it is what keeps a runaway fork loop from exhausting the process table of the node.

Keyword `pg_vmem_limit`

required:    false
scopable:    true
convert:     size

Example:

pg_vmem_limit=1g

Description:

The memory plus swap the processes of the group may use, in bytes.

The Out-Of-Memory killer is triggered in case of tresspassing. The specified value must be greater than pg_mem_limit.

Keyword `post_provision`

required:    false
scopable:    true
rbac:        Triggers require the root grant.

Description:

A command or script to execute after the resource provision action.

Errors do not interrupt the action.

This trigger is only executed on leaders.

Keyword `post_unprovision`

required:    false
scopable:    true
rbac:        Triggers require the root grant.

Description:

A command or script to execute after the resource unprovision action.

Errors do not interrupt the action.

This trigger is only executed on leaders.

Keyword `pre_provision`

required:    false
scopable:    true
rbac:        Triggers require the root grant.

Description:

A command or script to execute before the resource provision action.

Errors do not interrupt the action.

Keyword `pre_unprovision`

required:    false
scopable:    true
rbac:        Triggers require the root grant.

Description:

A command or script to execute before the resource unprovision action.

Errors do not interrupt the action.

Keyword `provision`

required:    false
scopable:    false
default:     true
convert:     bool

Description:

Set to false to ignore the provision and unprovision actions on the resource.

Warning: provision and unprovision use data-destructive operations like formatting.

It is recommended to set provision=false on long-lived critical objects, to force administrators to remove this setting when they really want to destroy data.

Keyword `provision_requires`

required:    false
scopable:    false

Example:

provision_requires=ip#0 fs#0(down,stdby down)

Description:

A whitespace-separated list of conditions to meet to accept a ‘provision’ action.

A condition is expressed as <rid>(<state>,...).

If states are omitted, up,stdby up is used as the default expected states.

Keyword `recursive`

required:    false
scopable:    true
default:     false
convert:     bool
rbac:        Requires the root grant.

Description:

Also replicate the writable subvolumes nested in the src subvolume.

Each nested subvolume is sent on its own, and put back in place on the peer. The read-only subvolumes nested in src, as the snapshots a sync.btrfssnap resource takes, are not replicated.

Keyword `schedule`

required:    false
scopable:    true
rbac:        A keyword of the btrfs driver, which needs the root grant to choose.

Example:

schedule=00:00-01:00 mon

Description:

Set the task run schedule.

See usr/share/doc/opensvc/schedule for the schedule syntax reference.

Keyword `shared`

required:    false
scopable:    true
convert:     bool

Description:

If true, the resource will be considered shared during provision and unprovision actions.

A shared resource driver can implement a different behaviour depending on weither it is run from the leader instance, or not:

When --leader is set, the driver creates and configures the system objects. For example the disk.disk driver allocates a SAN disk and discover its block devices.
When --leader is not set, the driver does not redo the actions already done by the leader, but may do some. For example, the disk.disk driver skips the SAN disk allocation, but discovers the block devices.

The daemon takes care of setting the --leader flags on the commands it submits during deploy, purge, provision and unprovision orchestrations.

Warning: If admins want to submit --local provision or unprovision commands themselves, they have to set the --leader flag correctly.

Flex objects usually don’t use shared resources. But if they do, only the flex primary gets --leader commands.

Warning: All resources depending on a shared resource must also be flagged as shared.

Keyword `src`

required:    true
scopable:    true
rbac:        Requires the root grant.

Example:

src={fs#1.label}:{fs#1.subvol}

Description:

Source subvolume of the sync, as <label>:<subvol>.

<label> is the label of the btrfs filesystem, which the sync finds the filesystem by on every node: the device of a filesystem may change from a node to another, its label does not. <subvol> is the path of the subvolume from the root of the filesystem.

Reference the fs.btrfs resource mounting it rather than repeating its values, as {fs#1.label}:{fs#1.subvol}, so the two can not drift apart.

Keyword `standby`

required:    false
scopable:    true
convert:     bool

Description:

If true, always start the resource, even on non-started instances.

The daemon is responsible for starting standby resources.

A resource can be set standby on a subset of nodes using keyword scoping.

A typical use-case is a synchronized filesystem on non-shared disks. The remote filesystem must be mounted to not overflow the underlying filesystem.

Warning: In most situation, don’t set shared resources standby, a non-clustered fs on shared disks for example.

Keyword `stat_timeout`

required:    false
scopable:    true
convert:     duration

Description:

The fs resources status evaluation includes a stat syscall test. This keyword defines the maximum wait time for those stat calls to respond.

When expired, the resource status is degraded is to warn, which can trigger a monitor action (reboot or crash the node) if the resource is monitored.

Keyword `subset`

required:    false
scopable:    true

Description:

The name of the subset this resource is assigned to.

Resources of a same driver group and a same subset are ordered and acted upon together, and are configured as a whole in a [subset#<group>:<name>] section, or in a less precise [subset#<name>] one.

That section accepts parallel, to act on the members concurrently rather than one after the other, and the pg_* keywords, to place the members in their own process group.

Keyword `tags`

required:    false
scopable:    true
convert:     set

Description:

A whitespace-separated list of tags.

Tags can be used for resource selection by tag.

Some tags can influence the driver behaviour:

noaction

Skip any state changing action on the resource and imply optional=true.
nostatus

Force the status n/a.

Keyword `target`

required:    true
scopable:    true
candidates:  nodes, drpnodes, local
convert:     list
rbac:        Requires the root grant.

Description:

Which nodes should receive this data sync from the PRD node where the instance is up and running.

target=local allows updating a dst subvolume of another filesystem on the same server that sends the data from the src subvolume.

Keyword `timeout`

required:    false
scopable:    true
convert:     duration
rbac:        Requires the root grant.

Example:

timeout=5m

Description:

Wait for <duration> before declaring the sync action a failure.

If no timeout is set, the agent waits indefinitely for the sync action to exit.

Keyword `type`

required:    false
scopable:    false
rbac:        Requires the root grant, except for the values store.

Description:

The resource driver name.

Keyword `unprovision`

required:    false
scopable:    false
default:     true
convert:     bool

Description:

Set to false to ignore the unprovision action on the resource.

Warning: unprovision use data-destructive operations like formatting.

It is recommended to set provision=false on long-lived critical objects, to force administrators to remove this setting when they really want to destroy data.

Keyword `unprovision_requires`

required:    false
scopable:    false

Example:

unprovision_requires=ip#0 fs#0(down,stdby down)

Description:

A whitespace-separated list of conditions to meet to accept a ‘unprovision’ action.

A condition is expressed as <rid>(<state>,...).

If states are omitted, up,stdby up is used as the default expected states.

Keyword `update_requires`

required:    false
scopable:    false
aliases:     sync_requires, sync_update_requires, sync_nodes_requires, sync_drp_requires

Example:

update_requires=ip#0 fs#0(down,stdby down)

Description:

A whitespace-separated list of conditions to meet to accept an ‘update’ or a ‘full’ action of a sync resource. A scheduled ‘update’ is not scheduled while they are not met.

A condition is expressed as <rid>(<state>,...).

If states are omitted, up,stdby up is used as the default expected states.

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