High Availability

High availability centers around RAID levels, redundancy, pre-emptive copy, dynamic spares, dedicated spares, and copyback. With high availability, the Oracle FS System can respond gracefully to an unexpected hardware or software failure that has the potential for service disruption. Furthermore, this feature keeps customer data highly accessible even during hardware replacements.

The Oracle FS System includes the following high‑availability features:

Single Parity

Stores the original user data plus one set of parity bits to help in the recovery of lost data. Access to the data is preserved even after the failure of one drive. Single parity is implemented using RAID 5 technology and is the default redundancy level for the Storage Classes that specify the performance-type media.

Double Parity

Stores the original user data plus two sets of parity bits to help in the recovery of lost data. Access to the data is preserved even after the simultaneous failure of two drives. Double parity is implemented using RAID 6 technology and is the default redundancy level for the Storage Classes that specify the capacity-type media.

Mirroring

A RAID level in which the Oracle FS System maintains an exact duplicate of a logical volume at a different location. No parity data is used. Mirroring protects against the loss of at least one drive and possibly more drives with an improvement of the performance of random write operations. Mirrored RAID is implemented using RAID 10 technology.

Oracle Pre-Emptive Copy

A feature of the Oracle FS System firmware that copies the data on a drive that has been predicted to fail to a spare drive before the suspect drive fails and is subsequently taken offline for replacement. This feature avoids performance degradation and potential exposure to data loss when the drive does fail.

Dynamic Spare

Unallocated strips on high-capacity hard disk drives (HDDs) in a given drive group. This spare capacity is striped across all of the HDDs in the drive group. Dynamic spares are used to support the RAID 5 protection level and the RAID 10 protection level. Dynamic spares cannot cross drive group boundaries.

Spare Drive

An unused solid state drive (SSD) that can support the rebuilding of a drive group by means of copy-away operations. Drive Enclosures and drive groups do not contain an SSD that is dedicated only to this purpose. If, however, an unused SSD exists in a Drive Enclosure and if an SSD in that Drive Enclosure fails or is removed, the system uses that unused drive to rebuild the drive that failed or was removed.

Furthermore, if no unused SSD exists, the system can use its parity data to continue functioning with a lost SSD.

Copyback

Copyback is the process of moving data from an active spare strip, for HDDs, or from a dedicated spare drive, for SSDs, to a newly replaced drive.