So what makes the Fusion system so reliable? Here are some key differences to traditional filesystems
- Data and Metadata Check-summing
- Self-Healing: Detecting and correcting Silent-Data-Errors with Scrub utility
- Atomic Transaction Writes: Data always being consistent, no need for repairing the file system.
Silent data corruption in traditional filesystem
- Small data corruption may happen at any time and in fact it does happen often, even on enterprise-class drives.
- Standard disks redundancy (RAID or mirror) does not protect against silent corruption.
- Filesystem receives damaged data that is further passed to an application which operates on corrupted data.
- Because application gets incorrect input its output is worthless as well.
- This may result in mistakes, damages and for mission-critical solutions even lawsuits and bankruptcies!
Silent data corruption prevention in ZFS
- Application issues a read. ZFS mirror tries first disk. Checksum reveals that the block is corrupted on the disk.
- ZFS tries second disk. Checksum indicates that the block is good.
- ZFS returns good data to the application and repairs the damaged block.