Backup Staging

ZMC Backup Staging

Regardless of the device type, the ZMC also allows you to define an optional write-cache mechanism called a staging area or holding disk, which stores the backup image on the server's hard disk. Because backups can be written in parallel to the holding disk, backups can be completed in much smaller windows than would be possible if writing directly to the device (even if the device is a virtual tape).  

In case of device/media failures (such as an unavailable S3 connection or running out of tapes in the changer), backups are stored in the staging area. The backup images stored in the staging area can be used for recovery and will be moved to the secondary media in next the backup run if the media problem is resolved.   

The staging area is used for Amanda source only if the whole backup image will fit in the staging area. Otherwise, source is directly written to the backup media volume without the use of staging area. Zmanda recommends the staging area size should be at least the size of one full backup image of all sources in the backup set. 

Staging Area Configuration

Device Name  

The name of the ZMC device used by the backup set. This information cannot be modified on this page.  

Backups run staged at  

The absolute path to the file staging area where backup images are collected before being archived. The default is /var/lib/amanda/staging/<backup set name>. The staging area directory must be accessible only by the amandabackup user. The staging area is used to provide better performance and an effective media fault tolerance. All backups from the client can be copied to the staging area in parallel.  The amount of parallelism depends on the Clients in parallel and other options on the Backup How page.  

AutoFlush   

Specifies whether Amanda should flush the backup images from the staging/area holding disk to the backup media before a backup run. The default value is enabled. You can change the default globally for all backup sets by changing the amanda.conf(5) file's autoflush no parameter to autoflush yes. You can monitor flush activity from the ZMC Monitor page.  
 
Enabling AutoFlush may require additional space on the media volumes to account for the previous backup runs, especially if you have set the Backup When Tapes/ Virtual Tapes Per Run value conservatively. If the Backup WhenTapes/ Virtual Tapes Per Run value is greater than 1, then the additional media will be used if it is required; if not the staging area must hold any backup images that exceed the limit. For example, consider a setup where a full backup usually fills up 3/4 of the medium.  If Tapes/Virtual Tapes Per Run is set to 1, you will usually end up with a separate piece of media for every backup, each filled to 3/4 capacity. If there happens to be a day where there are two backup images in a run, the staging area/holding disk must store the backup until there is a backup run with only one image that is less than one-quarter of the media size.  So if staging area space is at a premium and/or you wish to ensure that backup images always get saved to secondary media rather than the holding disk, you should set Tapes/Virtual Tapes Per Run accordingly.  

Staging size  

The controls allow you to allocate all space except a given amount, or no more than a given amount of space. Be sure to allocate enough space to hold at least a full backup.  

Partition total space/ Partition free space  

The total space and free space in the partition that contains the staging areas. This is only for information.  

Reserve for Incremental  

When space on a staging area falls below a threshold size (the value of this parameter), Amanda limits itself to performing only incremental backups. A threshold of 20 percent causes Amanda fall back to incremental backups when holding disk(s) free space falls below 20 percent. When there is a media error during a backup run, the backup images are still stored in the staging area. Amanda allows recovery from holding disk and backup media.  

Important Note:  

Do not attempt to back up the staging area. Use Exclude options if necessary to prevent any backup set from including a staging area for itself or any other backup set.