Saturday, June 26, 2010

Avamar Retention

Retention.

Ther are two types of retention in Avamar, basic and advanced. Basic retention policy can be specified in three ways:

Retention Period: Allows you to define how long a backup should be maintained. Length can be defined in days, weeks, months or years. The retention period is calculated from the start time. So if a job started on 3/31/2010 11:00 PM but ends on 4/1/2010 5:00 AM, the retention period will use 3/31/2010 to calculate when to expire the job.

End Date: Expire jobs on this particular date. This is not a moving backup window, and all jobs that have this retention policy will expire on the defined date. This is good for one time backup jobs where a system may need to be backed up, but after a certain date its backups are no longer necessary.

No end data: Backups never expire.

The second type of retention in Avamar, advanced, allows you to define how long to keep backups based on how they are tagged. Backup jobs can be tagged as daily, weekly, monthly and yearly. Every backup job is a daily job and is marked with a "D". If a backup was made on a Sunday, it is tagged with a "W" to signify it is a weekly. The very first backup job of the month is marked as an "M" which stands for monthly. The very first backup job of the year is marked with a "Y" for yearly. Tags can be combined for backup jobs to create layers of retention. The first backup job of any system is tagged as "DWMY". Jobs made on a Sunday are tagged "DW", while the first backup of the month is marked "DM" if it is not on a Sunday, which is then tagged with a "DWM".

Retention periods for each tag can be defined in days, weeks, months and years. The job expires when it is older than the time period defined in the retention policy. For example, if advanced retention policy is set to D: 20 days, Weekly: 40 days, Monthly: 100 days and Yearly: 365 days, and a job is tagged as DWMY, the D tag drops off after 20 days, W tag after 40 days, and Monthly tag after 100 days. If you look at the job after 100 days, it will have only one tag, Y. After 365 days, the job will expire.

According to the best practices guide for Avamar 5.0, weekly backups are equal to three daily backups, and a monthly backup is equal to six daily backups. This helps conserve space by reducing the amount of data that is kept on the system. But, this also reduces the amount of days you can go back to recover data from.

One important thing to note about advanced retention is that it does not apply to on demand and client initiated backups.
On demand jobs have an option to specify basic retention just before initiating the job. Client initiated backups use the End Use On Demand Retention. Both jobs get tagged with an "N" which stands for not tagged.

These tags can be changed by going to a job under Backup Management and selecting what tags you want to apply to a job. A job marked weekly, can be changed to daily, monthly, yearly, or a combination of all four tags. When jobs run as scheduled jobs, they are automatically tagged. If only basic retention is enabled, the jobs are still tagged, but only the expiration date is used to expire the job.

The best practice for retention is to use advanced retention since it saves data. Another best practice is to set minimum retention to 14 days for all jobs. This is because retention can only be specified in time periods. There is no setting in Avamar to not delete the very last backup job, or only delete a job until a new backup becomes available. If there is a problem with backing up a client, and retention is set to 7 days, it is likely that the failure can go unnoticed and all backups will be deleted. Setting minimum retention to 14 days buys some time for the admin to check if a job failed and if so why.

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