Table of contents
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 backup run if the media problem is resolved.
The staging area is used for Amanda DLE only if the whole backup image will fit in the staging area. Otherwise, DLE 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 DLEs in the backup set.
View Staging Area
The above table shows staging areas used by each backup set. The Device column whether it is a Disk or Tape or Amazon S3 backup. Flush column indicates if the previous backup images in the staging area are moved to backup media before the current backup run automatically. The location of staging area, disk space used, amount of data used in staging area are also displayed.
Staging Area Configuration
Device Name
The name of the ZMC device used by the backup set. This information cannot be modified in this page.
Enabling Auto Flush may require additional space on the media volumes to account for previous backup runs, especially if you have set the Backup When Tapes/Virtual Tapes Per Run value conservatively. If the Backup When Tapes/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 pieces of media for every backup, each fiilled 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.
Reserve for Incrementals
- 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% causes Amanda fall back to incremental backups when holding disk(s) free space falls below 20%.
- 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.
Staging Area Contents
This pane shows the space used for staging area for this backup set and list of files in the staging area.