Create incremental-mysql-backups-and-restores.md

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docs/incremental-mysql-backups-and-restores.md

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+# Incremental MySQL Backups and Restores
+
+Customers who have large MySQL databases who wish to save storage space can use the `--incremental` flag with `ghe-backup` and `ghe-restore`.
+Using this flag performs backups for other parts of GHES as normal, but only performs a MySQL backup of the changes to the database from the previous snapshot. 
+For larger databases this can conserve a lot of storage space for backups.
+
+## Configuring number of backups
+
+In your backup.config file you will need to set the variable `GHE_INCREMENTAL_BACKUP_MAX`.
+This variable determines how many cycles of full and incremental backups will be performed before the next full backup is performed with another cycle of incremental backups. 
+If `GHE_INCREMENTAL_BACKUP_MAX` is set to 14, backup-utils will run 1 full backup and then 13 incremental backups before performing another full backup on the next cycle.
+
+Incremental backups require the previous snapshot backups before them to work.
+Because of this, they do not follow the pruning strategy based on `GHE_NUM_SNAPSHOTS`.
+
+## Performing incremental backups
+
+To perform incremental backups:
+
+`bin/ghe-backup --incremental`
+
+the program will detect whether it needs to performa full or incremental snapshot based on what is currently in `GHE_DATA_DIR`. 
+
+To see what snapshots are part of your full and incremental backups, you can reference `GHE_DATA_DIR/inc_full_backup` and `GHE_DATA_DIR/inc_snapshot_data`, respectively.
+
+## Performing incremental restores
+to perform incremental restores:
+`bin/ghe-restore --incremental -s <snapshot-id>.  
+the program will use the mysql folders from each previous incremental backup and the full backup to restore the database.
+
+:warning: Incremental restores require the other snapshots in the cycle to complete a restore. Erasing snapshot directories that are part of a cycle corrupts the restore and makes it impossible to complete for the mySQL database.
+
+### Previous cycles
+To ensure there is a rolling window of mySQL backups, incremental mySQL backups from the cycle before the current one are kept.  Those snapshots are pre-pended with `inc_previous`. To perform a restore from there , just use the full directory name for the snapshot id.