doc: move replication_mode to top of configuration page reference
This commit is contained in:
Alex Auvolat
parent
939d1f2e17
commit
cfa5550cb2
@ -8,6 +8,8 @@ weight = 20
|
||||
Here is an example `garage.toml` configuration file that illustrates all of the possible options:
|
||||
|
||||
```toml
|
||||
replication_mode = "3"
|
||||
|
||||
metadata_dir = "/var/lib/garage/meta"
|
||||
data_dir = "/var/lib/garage/data"
|
||||
metadata_fsync = true
|
||||
@ -21,8 +23,6 @@ sled_cache_capacity = "128MiB"
|
||||
sled_flush_every_ms = 2000
|
||||
lmdb_map_size = "1T"
|
||||
|
||||
replication_mode = "3"
|
||||
|
||||
compression_level = 1
|
||||
|
||||
rpc_secret = "4425f5c26c5e11581d3223904324dcb5b5d5dfb14e5e7f35e38c595424f5f1e6"
|
||||
@ -134,6 +134,89 @@ The `[admin]` section:
|
||||
|
||||
### Top-level configuration options
|
||||
|
||||
#### `replication_mode` {#replication_mode}
|
||||
|
||||
Garage supports the following replication modes:
|
||||
|
||||
- `none` or `1`: data stored on Garage is stored on a single node. There is no
|
||||
redundancy, and data will be unavailable as soon as one node fails or its
|
||||
network is disconnected. Do not use this for anything else than test
|
||||
deployments.
|
||||
|
||||
- `2`: data stored on Garage will be stored on two different nodes, if possible
|
||||
in different zones. Garage tolerates one node failure, or several nodes
|
||||
failing but all in a single zone (in a deployment with at least two zones),
|
||||
before losing data. Data remains available in read-only mode when one node is
|
||||
down, but write operations will fail.
|
||||
|
||||
- `2-dangerous`: a variant of mode `2`, where written objects are written to
|
||||
the second replica asynchronously. This means that Garage will return `200
|
||||
OK` to a PutObject request before the second copy is fully written (or even
|
||||
before it even starts being written). This means that data can more easily
|
||||
be lost if the node crashes before a second copy can be completed. This
|
||||
also means that written objects might not be visible immediately in read
|
||||
operations. In other words, this mode severely breaks the consistency and
|
||||
durability guarantees of standard Garage cluster operation. Benefits of
|
||||
this mode: you can still write to your cluster when one node is
|
||||
unavailable.
|
||||
|
||||
- `3`: data stored on Garage will be stored on three different nodes, if
|
||||
possible each in a different zones. Garage tolerates two node failure, or
|
||||
several node failures but in no more than two zones (in a deployment with at
|
||||
least three zones), before losing data. As long as only a single node fails,
|
||||
or node failures are only in a single zone, reading and writing data to
|
||||
Garage can continue normally.
|
||||
|
||||
- `3-degraded`: a variant of replication mode `3`, that lowers the read
|
||||
quorum to `1`, to allow you to read data from your cluster when several
|
||||
nodes (or nodes in several zones) are unavailable. In this mode, Garage
|
||||
does not provide read-after-write consistency anymore. The write quorum is
|
||||
still 2, ensuring that data successfully written to Garage is stored on at
|
||||
least two nodes.
|
||||
|
||||
- `3-dangerous`: a variant of replication mode `3` that lowers both the read
|
||||
and write quorums to `1`, to allow you to both read and write to your
|
||||
cluster when several nodes (or nodes in several zones) are unavailable. It
|
||||
is the least consistent mode of operation proposed by Garage, and also one
|
||||
that should probably never be used.
|
||||
|
||||
Note that in modes `2` and `3`,
|
||||
if at least the same number of zones are available, an arbitrary number of failures in
|
||||
any given zone is tolerated as copies of data will be spread over several zones.
|
||||
|
||||
**Make sure `replication_mode` is the same in the configuration files of all nodes.
|
||||
Never run a Garage cluster where that is not the case.**
|
||||
|
||||
The quorums associated with each replication mode are described below:
|
||||
|
||||
| `replication_mode` | Number of replicas | Write quorum | Read quorum | Read-after-write consistency? |
|
||||
| ------------------ | ------------------ | ------------ | ----------- | ----------------------------- |
|
||||
| `none` or `1` | 1 | 1 | 1 | yes |
|
||||
| `2` | 2 | 2 | 1 | yes |
|
||||
| `2-dangerous` | 2 | 1 | 1 | NO |
|
||||
| `3` | 3 | 2 | 2 | yes |
|
||||
| `3-degraded` | 3 | 2 | 1 | NO |
|
||||
| `3-dangerous` | 3 | 1 | 1 | NO |
|
||||
|
||||
Changing the `replication_mode` between modes with the same number of replicas
|
||||
(e.g. from `3` to `3-degraded`, or from `2-dangerous` to `2`), can be done easily by
|
||||
just changing the `replication_mode` parameter in your config files and restarting all your
|
||||
Garage nodes.
|
||||
|
||||
It is also technically possible to change the replication mode to a mode with a
|
||||
different numbers of replicas, although it's a dangerous operation that is not
|
||||
officially supported. This requires you to delete the existing cluster layout
|
||||
and create a new layout from scratch, meaning that a full rebalancing of your
|
||||
cluster's data will be needed. To do it, shut down your cluster entirely,
|
||||
delete the `custer_layout` files in the meta directories of all your nodes,
|
||||
update all your configuration files with the new `replication_mode` parameter,
|
||||
restart your cluster, and then create a new layout with all the nodes you want
|
||||
to keep. Rebalancing data will take some time, and data might temporarily
|
||||
appear unavailable to your users. It is recommended to shut down public access
|
||||
to the cluster while rebalancing is in progress. In theory, no data should be
|
||||
lost as rebalancing is a routine operation for Garage, although we cannot
|
||||
guarantee you that everything will go right in such an extreme scenario.
|
||||
|
||||
#### `metadata_dir` {#metadata_dir}
|
||||
|
||||
The directory in which Garage will store its metadata. This contains the node identifier,
|
||||
@ -287,89 +370,6 @@ The value of this parameter is the maximum size the metadata database can take.
|
||||
This value is not bound by the physical RAM size of the machine running Garage.
|
||||
If not specified, it defaults to 1GiB on 32-bit machines and 1TiB on 64-bit machines.
|
||||
|
||||
#### `replication_mode` {#replication_mode}
|
||||
|
||||
Garage supports the following replication modes:
|
||||
|
||||
- `none` or `1`: data stored on Garage is stored on a single node. There is no
|
||||
redundancy, and data will be unavailable as soon as one node fails or its
|
||||
network is disconnected. Do not use this for anything else than test
|
||||
deployments.
|
||||
|
||||
- `2`: data stored on Garage will be stored on two different nodes, if possible
|
||||
in different zones. Garage tolerates one node failure, or several nodes
|
||||
failing but all in a single zone (in a deployment with at least two zones),
|
||||
before losing data. Data remains available in read-only mode when one node is
|
||||
down, but write operations will fail.
|
||||
|
||||
- `2-dangerous`: a variant of mode `2`, where written objects are written to
|
||||
the second replica asynchronously. This means that Garage will return `200
|
||||
OK` to a PutObject request before the second copy is fully written (or even
|
||||
before it even starts being written). This means that data can more easily
|
||||
be lost if the node crashes before a second copy can be completed. This
|
||||
also means that written objects might not be visible immediately in read
|
||||
operations. In other words, this mode severely breaks the consistency and
|
||||
durability guarantees of standard Garage cluster operation. Benefits of
|
||||
this mode: you can still write to your cluster when one node is
|
||||
unavailable.
|
||||
|
||||
- `3`: data stored on Garage will be stored on three different nodes, if
|
||||
possible each in a different zones. Garage tolerates two node failure, or
|
||||
several node failures but in no more than two zones (in a deployment with at
|
||||
least three zones), before losing data. As long as only a single node fails,
|
||||
or node failures are only in a single zone, reading and writing data to
|
||||
Garage can continue normally.
|
||||
|
||||
- `3-degraded`: a variant of replication mode `3`, that lowers the read
|
||||
quorum to `1`, to allow you to read data from your cluster when several
|
||||
nodes (or nodes in several zones) are unavailable. In this mode, Garage
|
||||
does not provide read-after-write consistency anymore. The write quorum is
|
||||
still 2, ensuring that data successfully written to Garage is stored on at
|
||||
least two nodes.
|
||||
|
||||
- `3-dangerous`: a variant of replication mode `3` that lowers both the read
|
||||
and write quorums to `1`, to allow you to both read and write to your
|
||||
cluster when several nodes (or nodes in several zones) are unavailable. It
|
||||
is the least consistent mode of operation proposed by Garage, and also one
|
||||
that should probably never be used.
|
||||
|
||||
Note that in modes `2` and `3`,
|
||||
if at least the same number of zones are available, an arbitrary number of failures in
|
||||
any given zone is tolerated as copies of data will be spread over several zones.
|
||||
|
||||
**Make sure `replication_mode` is the same in the configuration files of all nodes.
|
||||
Never run a Garage cluster where that is not the case.**
|
||||
|
||||
The quorums associated with each replication mode are described below:
|
||||
|
||||
| `replication_mode` | Number of replicas | Write quorum | Read quorum | Read-after-write consistency? |
|
||||
| ------------------ | ------------------ | ------------ | ----------- | ----------------------------- |
|
||||
| `none` or `1` | 1 | 1 | 1 | yes |
|
||||
| `2` | 2 | 2 | 1 | yes |
|
||||
| `2-dangerous` | 2 | 1 | 1 | NO |
|
||||
| `3` | 3 | 2 | 2 | yes |
|
||||
| `3-degraded` | 3 | 2 | 1 | NO |
|
||||
| `3-dangerous` | 3 | 1 | 1 | NO |
|
||||
|
||||
Changing the `replication_mode` between modes with the same number of replicas
|
||||
(e.g. from `3` to `3-degraded`, or from `2-dangerous` to `2`), can be done easily by
|
||||
just changing the `replication_mode` parameter in your config files and restarting all your
|
||||
Garage nodes.
|
||||
|
||||
It is also technically possible to change the replication mode to a mode with a
|
||||
different numbers of replicas, although it's a dangerous operation that is not
|
||||
officially supported. This requires you to delete the existing cluster layout
|
||||
and create a new layout from scratch, meaning that a full rebalancing of your
|
||||
cluster's data will be needed. To do it, shut down your cluster entirely,
|
||||
delete the `custer_layout` files in the meta directories of all your nodes,
|
||||
update all your configuration files with the new `replication_mode` parameter,
|
||||
restart your cluster, and then create a new layout with all the nodes you want
|
||||
to keep. Rebalancing data will take some time, and data might temporarily
|
||||
appear unavailable to your users. It is recommended to shut down public access
|
||||
to the cluster while rebalancing is in progress. In theory, no data should be
|
||||
lost as rebalancing is a routine operation for Garage, although we cannot
|
||||
guarantee you that everything will go right in such an extreme scenario.
|
||||
|
||||
#### `compression_level` {#compression_level}
|
||||
|
||||
Zstd compression level to use for storing blocks.
|
||||
|
||||
Loading…
Reference in New Issue
Block a user