Principles and computing method of Erasure Code for OceanStor 9000

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Erasure Code supports two data protection levels: N+M and N+M:B.
N+M includes N+1, N+2, N+3, and N+4, and is suitable for scenarios with a large number of nodes.
N+M:B includes N+2:1 and N+3:1, and is suitable for scenarios with a small number of nodes.
N+M indicates that each data stripe contains N original data strips and M redundant data strips, ensuring high data integrity even when M nodes fail.
N+M:B indicates that each data stripe contains N original data strips and M redundant data strips, ensuring high data integrity even when M disks or B nodes fail.
Users only need to specify +M or +M:B for directories or files. OceanStor 9000 automatically selects the most appropriate N value based on the number of nodes. N ranges from 2 to 16, and M from 1 to 4.
To configure the redundancy ratio:
1. Log in to DeviceManager.
2. Choose Provisioning > Resource Manager.
3. On the page that is displayed, select a directory and click Properties.
4. In the dialog box that is displayed, click the Redundancy Ratio tab and set +RDC/RDN.
In N+M scenarios, data slices are stored on N nodes, and redundant data is stored on another M nodes. Among the N+M nodes, up to three are allowed to fail at the same time. However, N is within 2 to 16 and OceanStor 9000 supports a maximum of 288 nodes. Accordingly, some nodes (except the N+M nodes) do not store data slices, and the failure of these nodes, in theory, does not impact on data integrity.
In N+M:B scenarios, data slices are stored on some disks of N nodes, and M pieces of redundant data are stored on other disks of the N nodes. The system allows up to M pieces of redundant data to be lost. That is, M disks are allowed to fail at the same time. Similarly, if more than B nodes fail, more than M pieces of redundant data will be lost. Therefore, a maximum of M disks or B nodes are allowed to fail.

Other related questions:
Computing Erasure Code for OceanStor 9000
Computing Erasure Code for OceanStor 9000: In a normal read/write process, Erasure Code is computed at the CA layer. In a data recovery process, Erasure Code is computed at the OBS layer.

Code (RS, Raptor, or others) used by Erasure Code of OceanStor 9000
Huawei develops Erasure Code of OceanStor 9000 based on the array code and has the patent and intellectual property of the Erasure Code algorithm.

Obtaining documentation and application scenarios related to Erasure Code of OceanStor 9000
To obtain documentation related to Erasure Code of OceanStor 9000, see: - OceanStor 9000 V100R001C01 Administrator Guide 11 - OceanStor 9000 V100R001 Erasure Code Multimedia 03

Storage space usage of OceanStor 9000 when erasure coding technology is used
When the erasure coding (EC) technology is used, OceanStor 9000 calculates the storage space usage based on the following principles: 1. The system security space is 90%. 2. When small files are stored, file metadata takes up about 8% space of OceanStor 9000. When large files are stored, file metadata takes up insignificant space. For example, in 4+2 redundancy mode, the maximum storage space usage is calculated as follows: (1) Small file storage space usage = 90% x (1 �?8%) x 66.7% = 55% (2) Large file storage space usage = 90% x 66.7% = 60%

Computing data distribution for OceanStor 9000
Data distribution for OceanStor 9000 is computed by CA using the HASH algorithm based on the FID of a file and the offset and length of the current operation.

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