Add configurable disk write speed limit for backups (#74)

* Add configurable disk write speed limit for backups

config/config_system.go

@@ -75,6 +75,8 @@ type SystemConfiguration struct {
 	Sftp SftpConfiguration `yaml:"sftp"`
 
 	CrashDetection CrashDetection `yaml:"crash_detection"`
+
+	Backups Backups `yaml:"backups"`
 }
 
 type CrashDetection struct {
@@ -89,6 +91,18 @@ type CrashDetection struct {
 	Timeout int `default:"60" json:"timeout"`
 }
 
+type Backups struct {
+	// WriteLimit imposes a Disk I/O write limit on backups to the disk, this affects all
+	// backup drivers as the archiver must first write the file to the disk in order to
+	// upload it to any external storage provider.
+	//
+	// If the value is less than 1, the write speed is unlimited,
+	// if the value is greater than 0, the write speed is the value in MB/s.
+	//
+	// Defaults to 0 (unlimited)
+	WriteLimit int `default:"0" yaml:"write_limit"`
+}
+
 // Ensures that all of the system directories exist on the system. These directories are
 // created so that only the owner can read the data, and no other users.
 func (sc *SystemConfiguration) ConfigureDirectories() error {