NetBackup 7.1 Features - Auto Image Replication
Welcome to NetBackup 7.1! This series of blogs will provide additional information into the key features of NetBackup 7.1 continuing today with Auto Image Replication (AIR).
The growth in the use of disk storage (particularly deduplicating disk storage) for backup has highlighted a limitation of disk storage when it comes to disaster recovery. Tapes can easily be sent offsite to be used for restores after a site outage. Disk doesn’t offer this flexibility. Some OpenStorage technologies, including the PureDisk Deduplication Option, support “out of band” replication where the contents of the disk storage is replicated between devices – however NetBackup has no knowledge of the data which makes recovery in a NetBackup protected environment more difficult. Using this approach the replicated data can only be accessed after recreating the NetBackup catalog – which is done by importing the entire content of the disk storage at the remote site using the bpimport command. The nbcatsync utility, introduced in NetBackup 6.5.6 and 7.0.1 can address this challenge it relies on being able to restore the catalog from a catalog backup and then “post-process” it to reconcile the disk device mappings. While faster than importing the contents of the storage, this is still a time consuming process.
This has all changed with the introduction of AIR. The use of Storage Lifecycle Policies (SLP) and optimized duplication between disk pools allows disk based backups to be replicated between devices under NetBackup control. Prior to NetBackup 7.1 this process has been limited to the NetBackup master server from which they originated. With NetBackup 7.1 site to site disaster recovery – whether the site is two rooms in the same data center or separate data centers across the country - can now be done using two separate Masters and the process is automatic once the SLP has been configured. Obviously the greater the separation between the sites the greater the type and severity of disaster that can be protected against.
The Auto Image Replication (AIR) feature introduced in NetBackup 7.1 addresses the site to site replication challenge by allowing Storage Lifecycle Policies to duplicate selected images between NetBackup Master domains. Backups are first written to a Media Server Deduplication Pool (MSDP) using a suitably configured SLP and then duplicated to a remote target NetBackup domain. An SLP in the target domain logs the duplicated copy in the catalog of the target domain and it is held there on MSDP disk based on a retention policy set in the source SLP. Remember, this is a “duplication” process since the data is already “deduplicated” by using the MSDP.
The retention of the data at the target site is configured from the source site. This SLP can also be configured to duplicate imported data to other types of storage at the remote site, and then expire it from the disk it was duplicated to. For example, once the data is duplicated to the remote site, it can then be copied to a tape drive at the remote site for long term storage that NetBackup is “aware of”. This process could then free up space for additional replication from the source domain. At this time, the destination retention at the Target site is a fixed time period, however support for the “expire after duplication” and “capacity managed” retention options will be included in a future release.
The primary purpose of Auto Image Replication is to create off-site copies of mission critical backups to protect against site loss. It is not intended to extend the storage capacity of a backup domain by allowing backups to be stored in a separate domain, nor is the intention to provide for day to day restores of data. Due to WAN bandwidth restrictions between sites, typically only the most critical data should be chosen for duplication using AIR. Electronic off-siting in this manner allows the backup set to be duplicated to an off-site location as soon as the backup has completed at the primary site without the need for user intervention based on the configuration of the SLP. It also means that the duplicate copy is available at the disaster recovery site as soon as the duplication has completed. This offers a significant advantage over traditional tape based off-siting in which backups must be duplicated to tapes that are then removed from the tape library and shipped to the disaster recovery site, a time consuming and costly activity with a risk that the tapes could be lost or stolen in transit.
In order to use Auto Image Replication suitable disk storage devices must be configured in the source and target domains. In the NetBackup 7.1 release the Auto Image Replication feature only supports the Media Server Deduplication Option (MSDP) to duplicate backups between domains. Support for OpenStorage devices and PureDisk Deduplication Option are expected to follow in a future release.
How does it work? Auto Image Replication works by duplicating backups from a disk pool in the source domain to a disk pool in the target domain. The replication operation requires two SLPs, one in the source domain and one in the target domain, both of which must have the same name. The SLP in the source domain is associated with the backup policy and controls the writing of backup and the subsequent duplication to the target domain. The SLP in the target domain is not associated with a backup policy but is invoked by an alerting mechanism when a new image (duplicated from the source domain) is detected. This SLP runs the process to add the information about the backup to the target domain and can also be configured to duplicate the backup to other storage locations in the target domain.
An Auto Image Replication backup image is different to a normal NetBackup backup image because once the backup has completed the image database information associated with the backup (the part of the NetBackup catalog that lists what the backup actually contains) is appended to the end of the backup image before it is duplicated to the target domain. When a new backup is detected in the target domain this information is read from the backup and used to populate the target domain’s NetBackup catalog. This information only exists in the source domain copies and the initial copy in the target domain and is not included in any subsequent duplicate copies created in the target domain.
To help understand the process, refer to the following diagram and the numbered notes following the diagram.
The figure shows the sequence of events in an Auto Image Replication backup and duplication operation broken down into 4 discrete steps:
- Step 1 – The backup is written to disk storage in the source domain using a backup policy with an SLP configured for Auto Image Replication. When the backup completes the catalog data it generates is appended to the end of the backup.
- Step 2 – the backup is duplicated to the target domain across the WAN (or LAN)
- Step 3 – the storage device in the target domain alerts the target master server to the fact that a backup has been duplicated to it. This triggers the receiving SLP to run a “fast import” operation in which the catalog data transferred from the source domain is added to the target domain’s catalog.
- Step 4 – the receiving SLP in the target domain can now duplicate the received backup to any desired location for storage – such as creating a tape for long term retention.
Hopefully this information on Auto Image Replication has been helpful. Join us tomorrow for a look at another major NetBackup 7.1 feature – OpsCenter Reporting Enhancements including Deployment Analyzer for calculating Front End Terabyte (FETB) in existing NetBackup environments.