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The following tables are intended to guide you to choose the right combination of capabilities based on your requirements. It is common to want the most
|Gitaly Cluster | Very high - tolerant of node failures | RTO for a single node of 10s with no manual intervention | Data is stored on multiple nodes | Good - While writes may take slightly longer due to voting, read distribution improves read speeds | **Trade-off** - Slight decrease in write speed for redundant, strongly-consistent storage solution. **Risks** - [Does not currently support snapshot backups](gitaly/index.md#snapshot-backup-and-recovery-limitations), GitLab backup task can be slow for large data sets |
|Gitaly Shards | Single storage location is a single point of failure | Would need to restore only shards which failed | Single point of failure | Good - can allocate repositories to shards to spread load | **Trade-off** - Need to manually configure repositories into different shards to balance loads / storage space **Risks** - Single point of failure relies on recovery process when single-node failure occurs |
|Gitaly + NFS | Single storage location is a single point of failure | Single node failure requires restoration from backup | Single point of failure | Average - NFS is not ideally suited to large quantities of small reads / writes which can have a detrimental impact on performance | **Trade-off** - Easy and familiar administration though NFS is not ideally suited to Git demands **Risks** - Many instances of NFS compatibility issues which provide very poor customer experiences |
|Geo| Depends on the architecture of the Geo site. It is possible to deploy secondaries in single and multiple node configurations. | Eventually consistent. Recovery point depends on replication lag, which depends on a number of factors such as network speeds. Geo supports failover from a primary to secondary site using manual commands that are scriptable. | Geo currently replicates 100% of planned data types and verifies 50%. See [limitations table](geo/replication/datatypes.md#limitations-on-replicationverification) for more detail. | Improves read/clone times for users of a secondary. | Geo is not intended to replace other backup/restore solutions. Because of replication lag and the possibility of replicating bad data from a primary, we recommend that customers also take regular backups of their primary site and test the restore process. |
## Scenarios for failure modes and available mitigation paths
The following table outlines failure modes and mitigation paths for the product offerings detailed in the tables above. Note - Gitaly Cluster install assumes an odd number replication factor of 3 or greater
| Gitaly Mode | Loss of Single Gitaly Node | Application / Data Corruption | Regional Outage (Loss of Instance) | Notes |
| Single Gitaly Node | Downtime - Must restore from backup | Downtime - Must restore from Backup | Downtime - Must wait for outage to end | |
| Single Gitaly Node + Geo Secondary | Downtime - Must restore from backup, can perform a manual failover to secondary | Downtime - Must restore from Backup, errors could have propagated to secondary | Manual intervention - failover to Geo secondary | |
| Sharded Gitaly Install | Partial Downtime - Only repositories on impacted node affected, must restore from backup | Partial Downtime - Only repositories on impacted node affected, must restore from backup | Downtime - Must wait for outage to end | |
| Sharded Gitaly Install + Geo Secondary | Partial Downtime - Only repositories on impacted node affected, must restore from backup, could perform manual failover to secondary for impacted repositories | Partial Downtime - Only repositories on impacted node affected, must restore from backup, errors could have propagated to secondary | Manual intervention - failover to Geo secondary | |
| Gitaly Cluster Install* | No Downtime - will swap repository primary to another node after 10 seconds | Not applicable; All writes are voted on by multiple Gitaly Cluster nodes | Downtime - Must wait for outage to end | Snapshot backups for Gitaly Cluster nodes not supported at this time |
| Gitaly Cluster Install* + Geo Secondary | No Downtime - will swap repository primary to another node after 10 seconds | Not applicable; All writes are voted on by multiple Gitaly Cluster nodes | Manual intervention - failover to Geo secondary | Snapshot backups for Gitaly Cluster nodes not supported at this time |
