Advanced (GFS) Retention

Categories: Alike v3, Backup Scheduling


Basic retention has been part of the Alike product since its inception and is the default mechanism for all backups. Backups controlled by Basic retention will retain 2 versions of the VM. Alike Standard and DR users can increase the number of versions retained across all VMs under Settings->Advanced (‘Default versions retained per VM’).

In Alike Standard and DR, it’s also possible to customize the number of versions retained per-VM. In the Explorer pane, select the VM and click “VM Protection Options”, and then increase the “Local Versions to Retain”. Users of Alike DR can also increase the “Offsite Versions Retained” if they are using the Offsite Vaulting feature, making it possible to retain a different number of versions onsite and offsite.

Retention And Schedules

Basic retention allows you to mix and match multiple schedules to protect the same VM. For example, you may back up a VM on one schedule during weekdays, and use another schedule on weekends. Your number to retain will apply across both schedules, meaning that if have set your retention to 5 versions, Alike will purge the oldest after 5 backups, no matter which schedule is run. Thus, Basic retention is applied per VM.

For Advanced retention, you define a GFS policy that is applied per schedule. This means that Alike marks a VM from this backup as belong to the schedule every time it runs so that your GFS policies can be applied correctly. If you create another schedule containing the same VM, the GFS policy you defined in the first schedule will not apply.

You can think of your GFS policies as “belonging to” schedules, and think of Basic retention settings as “belonging to” VMs. You can combine the two freely, using GFS for regimented, long-term retention schemes, and Basic retention for everything else.

Tip: It’s best to only have one GFS schedule for a VM. Backing up the same VM with multiple schedules is fine, but it will be easiest to plan and understand if only one of those schedules uses GFS.

Advanced (GFS) Retention

GFS stands for Grandfather, Father, Son and is a popular scheme for traditional backup media rotation. While Alike has a global data deduplication store rather than a library of tapes, the GFS rotation system still provides a powerful way for backup versions to span long archiving periods efficiently.

GFS is based on a tiered promotion scheme of daily, weekly, monthly, and yearly backups. In the tape world, each tier is associated with a pool of cassettes whose quantity is strictly enforced. For example, a scheme may call for a pool of 5 dailies, 6 weeklies, 10 monthlies, and 5 yearlies, for a total of 26 tapes consumed at the very most.

Each week, a daily backup will be promoted to a weekly. If there are already 6 weekly collected, the oldest weekly will be dropped. Each month, a weekly will be promoted to a monthly. If there are already 10 monthlies, the oldest monthly will be dropped. Every year, a monthly will be promoted to a yearly, and if there are already 5 yearlies, the oldest yearly will be dropped. In this manner, backups are tiered out over a long time, with more backups weighted toward recent activity, tapering out to a predictable but sparser backup archive.


The image above is a screenshot from the “Advanced Retention Options” page under the Scheduling Wizard. From here, you can configure your GFS retention scheme and examine and calendar on the right in order to understand how your backups will be treated.

In the example above, we are looking at the end of the year, showing us dailies, weeklies, monthlies, and yearlies retained.

Understanding Promotion

Alike’s GFS scheme gives administrators considerable control over when a backup is promoted from one pool to the next. Let’s look at each pool or tier in detail.

  • Dailies: Dailies are always promoted from the last instance of the schedule’s run on that day. While it is fine to run a GFS schedule multiple times in a day, only one run of the schedule will be selected as your daily, and this will be the run closest to midnight on that day.
  • Weeklies: You may choose to promote a daily to a weekly from any day of the week. For example, you may choose to promote your Sunday backups to dailies. If Alike cannot find a Sunday backup due to a missed run or an error, it will choose the next closest, such as a Saturday backup, and treat that as your weekly instead.
  • Monthlies: In strict GFS, monthlies are promoted from a weekly backup. You may choose to promote either the first or last weekly of the month to your monthly. For example, if you are retaining Sunday weeklies, and promoting the last weekly of the month, GFS will select the last Sunday backup of the month as your monthly. Be aware that some months have more Sundays than others due to how 7-day weeks line up on the calendar. If you’d like to get a monthly as close to the end of the month as possible, consider lose GFS, described below.
  • Yearlies: Yearlies can be promoted from any month of the year, such as January, December, or your company’s financial year-end month.
Strict vs Loose GFS

Strict GFS promotes monthlies from weeklies as described above and is how “classic” GFS works. Loose GFS will promote monthlies from a daily backup closest to the beginning or end of the month, as per your preference. The advantage of loose GFS is the ability to get monthlies reliably on the 31st, 30th, 29th, or 28th, depending on when the month actually ends.

Controlling Quantity

Alike allows you to configure the number of versions retained in each pool. It is possible to overlap these pools in any configuration you desire; for example, you may keep 20 monthlies, so your monthlies and yearlies overlap; and you may keep 10 weeklies, so your monthlies and weeklies overlap. On the other hand, you may decide to keep fewer than 7 dailies or fewer than 4 weeklies. Alike does require that you retain at least one version in each tier.

Tip: Consider your scheduling of dailies carefully. If you want to retain 5 dailies over the workdays but not the weekends, be sure your schedule runs Monday through Friday and does not run on Saturday or Sunday.

Final Notes

Note on Configuration: GFS is configured on a per-schedule basis. To enable GFS for a schedule, navigate to the “Jobs” tab and either select “Create Job” or right-click on an existing job and select “Edit Scheduled Job”. On the second page of the Scheduling Wizard, click “Advanced Retention Options” to bring up the GFS screen shown above.

Easy To Install. Easy To Use. Free To Try.