ECS employs a hybrid model triple mirroring data, metadata, and indexing. Erasure coding is also used for enhanced data protection and reduction of storage overhead.
Erasure coding provides enhanced data protection from a disk or node failure that is storage efficient as compared to conventional protection schemes. The ECS storage engine implements the Reed Solomon 12+4 erasure-coding scheme, in which a chunk is broken into 12 data fragments and 4 coding fragments for parity. These 16 fragments are then dispersed across nodes at the local site. The data and coding fragments for each chunk are equally distributed across nodes in the cluster. For example, with 8 nodes, each node stores 2 of the 16 fragments. The storage engine can then reconstruct a chunk from any 12 fragments of the original 16.
One of the ECS nodes was manually shutdown. The GeoDrive tool load balanced the traffic across all the available nodes and the recorders bypassed the failed node. The node failure did not affect the write rate, video quality, or result in dropped video.
If running a mixed workload, these changes can adversely affect the other workloads that might be present on the cluster.