Backup versions: what's kept and for how long
Each backup adds a version that stores only what changed. The five most recent are kept, older ones are thinned to one per hour, day, week and month, and every new version is checked once it has been written.
Every backup a set makes becomes a version: a point in time you can restore from. A version looks like a full copy of your folders when you browse it, but it only stores what changed since the version before, so keeping many of them takes far less space than many full copies.
Only what changed is stored
The first backup of a set stores everything. After that, each backup stores only files that are new or have changed; anything unchanged is shared with earlier versions instead of being stored again. The same content is stored once even when it turns up in several files or folders of the set.
You can see this in Versions…: each row shows the date, how many files the version holds, how many were new, and how much new data it added out of the set's total size. See incremental backup.
How long versions are kept
Keeping every version for ever would fill any destination, so after each backup Storage Studio thins out older versions. A set keeps:
| What | How many |
|---|---|
| The most recent versions | 5 |
| One version per hour | for the last 24 hours that had a backup |
| One version per day | for the last 30 days that had a backup |
| One version per week | for the last 8 weeks that had a backup |
| One version per month | for the last 12 months that had a backup |
So for recent changes you can go back hour by hour, over the past month day by day, and over the past year month by month. Versions that fall outside all of these are removed from the destination, and the space they used is gradually freed. These rules are the same for every set and aren't changed from the window.
Flowchart outline: How versions are thinned out as they get older
- A new backup
- leads to A new version is stored
- A new version is stored
- leads to It's checked
- It's checked
- leads to Older versions are thinned out
- Older versions are thinned out
- leads to The 5 most recent are kept
- leads to One per hour for the last 24 hours with backups
- leads to One per day for the last 30 days with backups
- leads to One per week for the last 8 weeks with backups
- leads to One per month for the last 12 months with backups
Every version is checked
After each backup, Storage Studio checks the new version by reading back a sample of what it just stored and making sure it matches. While that happens the set shows Checking…, and when the check passes it shows Protected and the card says "Last backup … · verified". Check on the card runs the same check whenever you like.
- If the check finds a problem, the set shows Needs attention: "The backup was saved but its safety check didn't pass, so the newest version may be incomplete. Try "Back up now" again."
- If the check couldn't run at all — a brief network drop, for example — the backup still counts as saved and the set shows Protected, and the next backup is checked as usual.
What a version doesn't include
A version holds the files that could be read at the time. Items in the Trash, temporary files, cache folders and developer package folders are left out, and a file that was locked or in use is skipped rather than failing the whole backup. See Data Backup.
Starting over
Versions stay at the destination when you Remove destination (keeps stored versions) or switch a set to a new destination. Only Delete & start fresh…, or changing a cloud set's passphrase, removes them all — see Where a backup can go and The backup passphrase.
See also: Restoring from a backup · Backup version · What backup messages mean