Relationship between RAID creation and LUN creation on the storage device

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The LUN can be allocated only after the RAID is created. A LUN cannot be allocated to another LUN.

Other related questions:
Creation of RAID groups and LUNs not required on the OceanStor 9000 online lab
RAID groups and LUNs are not required by the OceanStor 9000 online lab. Different from traditional cluster storage or array storage devices, OceanStor 9000 provides disk arrays on the back end as a distributed file system for big data based on all x86 servers. The entire cluster is a big file system (root directory) where subdirectories and shares can be directly created to use storage space.

RAID parameter configuration
For details about creating a RAID group, refer to Creating a RAID Group for parameter configuration.

What are the differences among different write strategies for LUN creation?
When creating a LUN, you can customize the write strategy to write through, write back with mirroring, write back without mirroring, mandatory write back with mirroring, or mandatory write back without mirroring. The differences among these write strategies are as follows: ? Write through: Data is directly written to hard disks in the storage system; therefore, the hard disks are accessed during each write operation. This strategy features high reliability but is deficient in performance. ? Write back: Data is written to cache firstly, and during the I/O idle hours, data is written onto hard disks; therefore, the hard disks are not accessed during each write operation. This operation features high performance and contains risks in reliability. ? Write back with mirroring: Data is written to the local cache and the peer cache at the same time. ? Write back without mirroring: Data is directly written to the local cache. ? Mandatory write back with mirroring: Data is written to the local cache and the peer cache at the same time by force. ? Mandatory write back without mirroring: Data is directly written to the local cache by force.

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