mirror of
https://git.deuxfleurs.fr/Deuxfleurs/garage.git
synced 2024-11-13 11:41:07 +00:00
110 lines
5 KiB
Markdown
110 lines
5 KiB
Markdown
+++
|
|
title = "Recovering from failures"
|
|
weight = 50
|
|
+++
|
|
|
|
Garage is meant to work on old, second-hand hardware.
|
|
In particular, this makes it likely that some of your drives will fail, and some manual intervention will be needed.
|
|
Fear not! For Garage is fully equipped to handle drive failures, in most common cases.
|
|
|
|
## A note on availability of Garage
|
|
|
|
With nodes dispersed in 3 zones or more, here are the guarantees Garage provides with the 3-way replication strategy (3 copies of all data, which is the recommended replication mode):
|
|
|
|
- The cluster remains fully functional as long as the machines that fail are in only one zone. This includes a whole zone going down due to power/Internet outage.
|
|
- No data is lost as long as the machines that fail are in at most two zones.
|
|
|
|
Of course this only works if your Garage nodes are correctly configured to be aware of the zone in which they are located.
|
|
Make sure this is the case using `garage status` to check on the state of your cluster's configuration.
|
|
|
|
In case of temporarily disconnected nodes, Garage should automatically re-synchronize
|
|
when the nodes come back up. This guide will deal with recovering from disk failures
|
|
that caused the loss of the data of a node.
|
|
|
|
|
|
## First option: removing a node
|
|
|
|
If you don't have spare parts (HDD, SDD) to replace the failed component, and if there are enough remaining nodes in your cluster
|
|
(at least 3), you can simply remove the failed node from Garage's configuration.
|
|
Note that if you **do** intend to replace the failed parts by new ones, using this method followed by adding back the node is **not recommended** (although it should work),
|
|
and you should instead use one of the methods detailed in the next sections.
|
|
|
|
Removing a node is done with the following command:
|
|
|
|
```bash
|
|
garage layout remove <node_id>
|
|
garage layout show # review the changes you are making
|
|
garage layout apply # once satisfied, apply the changes
|
|
```
|
|
|
|
(you can get the `node_id` of the failed node by running `garage status`)
|
|
|
|
This will repartition the data and ensure that 3 copies of everything are present on the nodes that remain available.
|
|
|
|
|
|
|
|
## Replacement scenario 1: only data is lost, metadata is fine
|
|
|
|
The recommended deployment for Garage uses an SSD to store metadata, and an HDD to store blocks of data.
|
|
In the case where only a single HDD crashes, the blocks of data are lost but the metadata is still fine.
|
|
|
|
This is very easy to recover by setting up a new HDD to replace the failed one.
|
|
The node does not need to be fully replaced and the configuration doesn't need to change.
|
|
We just need to tell Garage to get back all the data blocks and store them on the new HDD.
|
|
|
|
First, set up a new HDD to store Garage's data directory on the failed node, and restart Garage using
|
|
the existing configuration. Then, run:
|
|
|
|
```bash
|
|
garage repair -a --yes blocks
|
|
```
|
|
|
|
This will re-synchronize blocks of data that are missing to the new HDD, reading them from copies located on other nodes.
|
|
|
|
You can check on the advancement of this process by doing the following command:
|
|
|
|
```bash
|
|
garage stats -a
|
|
```
|
|
|
|
Look out for the following output:
|
|
|
|
```
|
|
Block manager stats:
|
|
resync queue length: 26541
|
|
```
|
|
|
|
This indicates that one of the Garage node is in the process of retrieving missing data from other nodes.
|
|
This number decreases to zero when the node is fully synchronized.
|
|
|
|
|
|
## Replacement scenario 2: metadata (and possibly data) is lost
|
|
|
|
This scenario covers the case where a full node fails, i.e. both the metadata directory and
|
|
the data directory are lost, as well as the case where only the metadata directory is lost.
|
|
|
|
To replace the lost node, we will start from an empty metadata directory, which means
|
|
Garage will generate a new node ID for the replacement node.
|
|
We will thus need to remove the previous node ID from Garage's configuration and replace it by the ID of the new node.
|
|
|
|
If your data directory is stored on a separate drive and is still fine, you can keep it, but it is not necessary to do so.
|
|
In all cases, the data will be rebalanced and the replacement node will not store the same pieces of data
|
|
as were originally stored on the one that failed. So if you keep the data files, the rebalancing
|
|
might be faster but most of the pieces will be deleted anyway from the disk and replaced by other ones.
|
|
|
|
First, set up a new drive to store the metadata directory for the replacement node (a SSD is recommended),
|
|
and for the data directory if necessary. You can then start Garage on the new node.
|
|
The restarted node should generate a new node ID, and it should be shown with `NO ROLE ASSIGNED` in `garage status`.
|
|
The ID of the lost node should be shown in `garage status` in the section for disconnected/unavailable nodes.
|
|
|
|
Then, replace the broken node by the new one, using:
|
|
|
|
```bash
|
|
garage layout assign <new_node_id> --replace <old_node_id> \
|
|
-c <capacity> -z <zone> -t <node_tag>
|
|
garage layout show # review the changes you are making
|
|
garage layout apply # once satisfied, apply the changes
|
|
```
|
|
|
|
Garage will then start synchronizing all required data on the new node.
|
|
This process can be monitored using the `garage stats -a` command.
|