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@ -8,7 +8,8 @@ weight = 20
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Here is an example `garage.toml` configuration file that illustrates all of the possible options:
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```toml
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replication_mode = "3"
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replication_factor = 3
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consistency_mode = "consistent"
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metadata_dir = "/var/lib/garage/meta"
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data_dir = "/var/lib/garage/data"
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@ -90,7 +91,8 @@ Top-level configuration options:
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[`lmdb_map_size`](#lmdb_map_size),
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[`metadata_dir`](#metadata_dir),
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[`metadata_fsync`](#metadata_fsync),
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[`replication_mode`](#replication_mode),
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[`replication_factor`](#replication_factor),
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[`consistency_mode`](#consistency_mode),
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[`rpc_bind_addr`](#rpc_bind_addr),
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[`rpc_bind_outgoing`](#rpc_bind_outgoing),
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[`rpc_public_addr`](#rpc_public_addr),
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@ -133,11 +135,12 @@ The `[admin]` section:
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### Top-level configuration options
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#### `replication_mode` {#replication_mode}
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#### `replication_factor` {#replication_factor}
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Garage supports the following replication modes:
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The replication factor can be any positive integer smaller or equal the node count in your cluster.
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The chosen replication factor has a big impact on the cluster's failure tolerancy and performance characteristics.
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- `none` or `1`: data stored on Garage is stored on a single node. There is no
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- `1`: data stored on Garage is stored on a single node. There is no
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redundancy, and data will be unavailable as soon as one node fails or its
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network is disconnected. Do not use this for anything else than test
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deployments.
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@ -148,17 +151,6 @@ Garage supports the following replication modes:
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before losing data. Data remains available in read-only mode when one node is
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down, but write operations will fail.
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- `2-dangerous`: a variant of mode `2`, where written objects are written to
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the second replica asynchronously. This means that Garage will return `200
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OK` to a PutObject request before the second copy is fully written (or even
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before it even starts being written). This means that data can more easily
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be lost if the node crashes before a second copy can be completed. This
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also means that written objects might not be visible immediately in read
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operations. In other words, this mode severely breaks the consistency and
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durability guarantees of standard Garage cluster operation. Benefits of
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this mode: you can still write to your cluster when one node is
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unavailable.
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- `3`: data stored on Garage will be stored on three different nodes, if
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possible each in a different zones. Garage tolerates two node failure, or
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several node failures but in no more than two zones (in a deployment with at
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@ -166,55 +158,84 @@ Garage supports the following replication modes:
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or node failures are only in a single zone, reading and writing data to
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Garage can continue normally.
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- `3-degraded`: a variant of replication mode `3`, that lowers the read
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quorum to `1`, to allow you to read data from your cluster when several
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nodes (or nodes in several zones) are unavailable. In this mode, Garage
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does not provide read-after-write consistency anymore. The write quorum is
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still 2, ensuring that data successfully written to Garage is stored on at
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least two nodes.
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- `3-dangerous`: a variant of replication mode `3` that lowers both the read
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and write quorums to `1`, to allow you to both read and write to your
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cluster when several nodes (or nodes in several zones) are unavailable. It
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is the least consistent mode of operation proposed by Garage, and also one
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that should probably never be used.
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- `5`, `7`, ...: When setting the replication factor above 3, it is most useful to
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choose an uneven value, since for every two copies added, one more node can fail
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before losing the ability to write and read to the cluster.
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Note that in modes `2` and `3`,
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if at least the same number of zones are available, an arbitrary number of failures in
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any given zone is tolerated as copies of data will be spread over several zones.
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**Make sure `replication_mode` is the same in the configuration files of all nodes.
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**Make sure `replication_factor` is the same in the configuration files of all nodes.
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Never run a Garage cluster where that is not the case.**
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It is technically possible to change the replication factor although it's a
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dangerous operation that is not officially supported. This requires you to
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delete the existing cluster layout and create a new layout from scratch,
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meaning that a full rebalancing of your cluster's data will be needed. To do
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it, shut down your cluster entirely, delete the `custer_layout` files in the
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meta directories of all your nodes, update all your configuration files with
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the new `replication_factor` parameter, restart your cluster, and then create a
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new layout with all the nodes you want to keep. Rebalancing data will take
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some time, and data might temporarily appear unavailable to your users.
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It is recommended to shut down public access to the cluster while rebalancing
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is in progress. In theory, no data should be lost as rebalancing is a
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routine operation for Garage, although we cannot guarantee you that everything
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will go right in such an extreme scenario.
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#### `consistency_mode` {#consistency_mode}
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The consistency mode setting determines the read and write behaviour of your cluster.
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- `consistent`: The default setting. This is what the paragraph above describes.
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The read and write quorum will be determined so that read-after-write consistency
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is guaranteed.
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- `degraded`: Lowers the read
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quorum to `1`, to allow you to read data from your cluster when several
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nodes (or nodes in several zones) are unavailable. In this mode, Garage
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does not provide read-after-write consistency anymore.
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The write quorum stays the same as in the `consistent` mode, ensuring that
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data successfully written to Garage is stored on multiple nodes (depending
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the replication factor).
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- `dangerous`: This mode lowers both the read
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and write quorums to `1`, to allow you to both read and write to your
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cluster when several nodes (or nodes in several zones) are unavailable. It
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is the least consistent mode of operation proposed by Garage, and also one
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that should probably never be used.
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Changing the `consistency_mode` between modes while leaving the `replication_factor` untouched
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(e.g. setting your node's `consistency_mode` to `degraded` when it was previously unset, or from
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`dangerous` to `consistent`), can be done easily by just changing the `consistency_mode`
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parameter in your config files and restarting all your Garage nodes.
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The consistency mode can be used together with various replication factors, to achieve
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a wide range of read and write characteristics. Some examples:
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- Replication factor `2`, consistency mode `degraded`: While this mode
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technically exists, its properties are the same as with consistency mode `consistent`,
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since the read quorum with replication factor `2`, consistency mode `consistent` is already 1.
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- Replication factor `2`, consistency mode `dangerous`: written objects are written to
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the second replica asynchronously. This means that Garage will return `200
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OK` to a PutObject request before the second copy is fully written (or even
|
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|
before it even starts being written). This means that data can more easily
|
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|
|
be lost if the node crashes before a second copy can be completed. This
|
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|
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|
also means that written objects might not be visible immediately in read
|
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|
|
|
operations. In other words, this configuration severely breaks the consistency and
|
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|
|
|
durability guarantees of standard Garage cluster operation. Benefits of
|
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|
|
this configuration: you can still write to your cluster when one node is
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unavailable.
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The quorums associated with each replication mode are described below:
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| `replication_mode` | Number of replicas | Write quorum | Read quorum | Read-after-write consistency? |
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| ------------------ | ------------------ | ------------ | ----------- | ----------------------------- |
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| `none` or `1` | 1 | 1 | 1 | yes |
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| `2` | 2 | 2 | 1 | yes |
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| `2-dangerous` | 2 | 1 | 1 | NO |
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| `3` | 3 | 2 | 2 | yes |
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| `3-degraded` | 3 | 2 | 1 | NO |
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| `3-dangerous` | 3 | 1 | 1 | NO |
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Changing the `replication_mode` between modes with the same number of replicas
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(e.g. from `3` to `3-degraded`, or from `2-dangerous` to `2`), can be done easily by
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just changing the `replication_mode` parameter in your config files and restarting all your
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Garage nodes.
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It is also technically possible to change the replication mode to a mode with a
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different numbers of replicas, although it's a dangerous operation that is not
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officially supported. This requires you to delete the existing cluster layout
|
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|
|
|
and create a new layout from scratch, meaning that a full rebalancing of your
|
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|
cluster's data will be needed. To do it, shut down your cluster entirely,
|
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|
|
|
delete the `custer_layout` files in the meta directories of all your nodes,
|
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|
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update all your configuration files with the new `replication_mode` parameter,
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|
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restart your cluster, and then create a new layout with all the nodes you want
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to keep. Rebalancing data will take some time, and data might temporarily
|
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|
|
appear unavailable to your users. It is recommended to shut down public access
|
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|
|
to the cluster while rebalancing is in progress. In theory, no data should be
|
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lost as rebalancing is a routine operation for Garage, although we cannot
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guarantee you that everything will go right in such an extreme scenario.
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| `consistency_mode` | `replication_factor` | Write quorum | Read quorum | Read-after-write consistency? |
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| ------------------ | -------------------- | ------------ | ----------- | ----------------------------- |
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| `consistent` | 1 | 1 | 1 | yes |
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| `consistent` | 2 | 2 | 1 | yes |
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| `dangerous` | 2 | 1 | 1 | NO |
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| `consistent` | 3 | 2 | 2 | yes |
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| `degraded` | 3 | 2 | 1 | NO |
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| `dangerous` | 3 | 1 | 1 | NO |
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#### `metadata_dir` {#metadata_dir}
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Add a comment saying that arbitrarily large replication factors are now supported?
Added a note about replication factors higher than 3 in the listing