Immutable Backup
An immutable backup is a backup that cannot technically be changed, overwritten or deleted within a defined retention window — not even with administrative rights. It is implemented through hardened Linux repositories using file system attributes, or through Object Lock in the S3 protocol. In Veeam Backup & Replication the period is configurable from a minimum of 7 to a maximum of 9,999 days. Immutability is what separates a backup from genuine ransomware protection.
Immutable Backup in practice
The target picture is the 3-2-1-1-0 rule: three copies of the data on two different media types, one copy off-site, one copy offline, air-gapped or immutable — and zero errors in a verified recovery test. That last point is decisive, because a backup never restored is an assumption, not a protection. Technically Veeam implements immutability in the hardened repository: a dedicated Linux server with an XFS file system whose backup files carry an immutability attribute for the configured period, connected using single-use credentials that are not retained in the backup infrastructure after deployment.
Even a compromised backup server therefore cannot delete the data. The same XFS is the prerequisite for Fast Clone, which produces synthetic full backups without physically copying data — this requires reflink and CRC support, created for example with mkfs.xfs -b size=4096 -m reflink=1,crc=1. In the cloud, S3 Object Lock in compliance mode plays the same role.
One distinction matters: immutability protects against deletion and encryption, not against data exfiltration — that requires encryption and network segmentation. Alendris designs backup architectures with an immutable on-premises target and signs them off only after a documented restore test; in a project for a manufacturing company, immutable Veeam storage together with a segmented network formed the backbone of ransomware resilience.