Glossary
Bitrot
Data degradation due to accumulation of non-critical failures.
For example; bits of data are stored on a traditional HDD as areas of magnetic orientation. Over time or due to manufacturing defects these areas can lose their orientation.
This type of corruption is not typically detected in traditional Windows and Linux filesystems however ZFS can detect and repair such decay.
Compression
Compression reduces the disk space required to store your files. It is completely transparent and typically has no performance impact. (In most cases compression improves performance due to efficiencies in reading/writing to disk).
Data Resiliency
The term “data resiliency” refers to data’s ability to “bounce back” in situations where it is compromised.
We improve the resilience of our systems by the use of redundant hardware and a self-healing filesystem:
- Dual power supply units
- Dual Network / interconnect links
- Entire system replication/mirroring to a secondary location
- ZFS parity allows multiple disks to fail before data is lost
Data Protection
Technologies and processes put in place to protect from data loss.
This is covered in detail on the data protection page.
Parity
Parity data is used by OpenZFS to achieve disk redundancy.
If a drive in the array fails remaining data on the other drives can be combined with the parity data to reconstruct the missing data. Parity data is also used to protect from bitrot.
We use multiple disk parity where more than one disk can fail in any disk group (typically 10-15 disks) without data loss.
Replication / Mirroring
Mirror of data on a physically separate system located in a different datacentre.
High Capacity Storage Systems are deployed in pairs. Data is mirrored to a secondary via a replication task that occurs every evening.
Snapshot
A read-only copy of the filestore frozen at a point in time.
Rather than run a traditional backup we use snapshots to create recovery points that can be used to recover old versions of your files. These are created every hour.
OpenZFS
OpenZFS is a filesystem and volume manager created by Sun Microsystems in 2005. The features of ZFS include protection against data corruption, support for high storage capacities, efficient data compression, snapshots continuous integrity checking and automatic repair.