Understanding data retention settings on a ShadowProtect BDR
Posted by Kevin Hoffman, Last modified by Tami Sutcliffe on Jun 23, 2016 02:23 PM
The BDR empowers you to take bare-metal backup of servers and desktops and store these backups locally on the BDR appliance. The bare-metal backups are powered by StorageCraft ShadowProtect in continuous incremental mode. Both the StorageCraft ImageManager and the backup manager software settings govern how much historical data is retained. The ImageManager settings are the main settings that determine data retention, and the backup manager settings determine extra data retention in addition to the ImageManager.
This article describes the data retention settings that are applicable to each way that you might be using bare-metal backups with the BDR. Please note that the data retention settings for file-level backups are different---they are always only determined by the versioning settings within the file-level backup manager.
Bare-metal Backups in Continuous Incremental Mode
First, an overview of how ShadowProtect backups in continuous incremental mode Work. ShadowProtect will take a base image file (*.spf) that represents the full backup of each volume (compressed). Then, every time it takes a backup of a volume, it generates an incremental file (*.spi) that represents the changes between the time when the backup was taken and the last time the backup was taken. In other words, every (successful) backup depends on the previous (successful) backup. In this fashion a "backup chain" is created that allows you to restore any point in time from the present back to when the original base image was taken.
Just by itself, this mechanism is insufficient for practical backups. This is the reason for the ImageManager. The ImageManager will take these backup files where one file depends on the previous file, and consolidates them into daily (*-cd.spi), weekly (*-cw.spi), and monthly (*-cm.spi) point-in-time representations of a delta. Thus, instead of a backup having to rely on thousands of incremental backups between the base image and the current point in time, it only needs to rely on hourly images until the last daily, daily images until the last month, and monthly images until the original base image. This allows older hourly, daily, and weekly image files to be deleted.
Another critical function of the ImageManager is that it verifies the integrity of both the data and the backup chain. When the image manager performs consolidation, and at frequent other intervals, it will read the contents of the backed up data and compare it against a cryptographic checksum (*.md5) to ensure that there hasn't been any silent data corruption between the time when the backup was generated and the consolidated representation of that data.
Bare-metal Backup Data Retention Settings Overview
The StorageCraft ImageManager settings determine how long to retain hourly, daily, and weekly point-in-time snapshots of the bare-metal images. These consolidation settings are set on a per server (or desktop) basis using the ImageManager user interface. The ImageManager allows you to set consolidation settings for the number of days to retain intra-daily (hourly) images, the number of days to retain daily images, and the number of days to retain weekly images.
VERY IMPORTANT: If you are backing up your bare-metal images off-site, you must keep at least 35 days of daily versions in the ShadowProtect ImageManager settings. This is because the off-site backup is retaining the base image plus the daily images plus the monthly images. (It does not retain weekly images to save on bandwidth.) Thus, you must keep at least a full month's worth of daily images to ensure that you chain in the cloud backup is complete.
The backup manager settings for the Number of Days to Keep Deleted Files (which is distinct from the ImageManager settings) will also affect data retention for bare-metal backup images kept in the off-site backups. When the ImageManager decides that it is time to delete a daily image file, the next time the off-site backup runs it will "mark" that file as deleted. That deleted file will then be retained in the off-site backup according to the Number of Days to Keep Deleted Files setting. We normally recommend setting the Number of Days to Keep Deleted Files settings to be 7 days.
Note that if you are replicating data between BDRs, then additionally you also must configure the ImageManager on the target BDR, and the ImageManager settings on the target BDR will determine data retention on the target BDR. The ImageManager settings on the target BDR can be different than the ImageManager settings on the source BDR.
Data Retention Settings for Local-only Bare-metal Backups to the BDR
If you are performing bare-metal backups of computers to the BDR, but are not backing up these bare-metal images any further, then you can change the ImageManager settings to whatever you like. Even in this case, we recommend setting the ImageManager number of days to retain daily images to be no less than 35 days.
Data Retention Settings for Bare-metal Backups to the BDR that are also Backed Up Offsite
In this scenario, bare-metal backups are stored on the BDR and consolidated by the ImageManager. You must make sure that the ImageManager setting for the number of days to keep daily images is at least 35 days (the default is 90 days). You can choose whichever values you like for the ImageManager retention settings for intra-daily (hourly) and weekly images, which will affect the disk space used on the BDR but will not affect the size of off-site backups.
Note that this scenario is also applicable if you are performing bare-metal backups to the BDR and then are also using the backup manager to backup the ShadowProtect data to a local USB drive or NAS device.
Data Retention Settings for Bare-metal Backups to the BDR that are Replicated
When replicating bare-metal backup images from one BDR to another BDR or Windows server, the ImageManager settings on the source BDR will affect disk space used on the source BDR. You should make sure the ImageManager setting for the number of days to keep daily images is at least 35 days.
The backup manager Number of Days to Keep Deleted Files setting (which is distinct from the ImageManager setting) is also applicable here just as with off-site backups. The replication target will retain daily images that are deleted on the source BDR for an additional period of time, according to the value of this setting. We recommend choosing 7 days.
The ImageManager must also be setup on the replication target BDR to perform consolidation of the ShadowProtect data on the target BDR. The reason is that according to your replication policy only the base image plus the daily images (daily policy) or the hourly images (realtime policy) are sent to the replication target. The replication target must therefore consolidate this information into the weekly and monthly images. The ImageManager settings on the replication target will determine how long the hourly, daily, and weekly images are retained for. If the replication target is being backed up to the cloud using the backup manager, you must ensure that the ImageManager number of days to keep daily images setting is at least 35 days.