Basic Concepts

Get yourself started with basic concepts.

• Disk domain

  A domain consisting of the same or different types of disks. Disk domains are isolated from each other. Therefore, services carried by different disk domains do not affect each other in terms of performance and faults if any.

• Storage pool

  A storage resource container created under a disk domain. The storage resources used by application servers are called up from these storage pools.

• Storage tier

  A set of storage media providing the same performance in a storage pool. Storage tiers are used to manage storage media with different performance and provide appropriate storage space for applications having different performance demands.

• Chunk (CK)

  A set of consecutive physical spaces of a fixed size on a disk.

• Chunk group (CKG)

  A logical set of CKs on different disks. A CKG has the properties of a redundant array of independent disks (RAID) group.

• Block virtualization

  A new type of RAID technology. Block virtualization divides disks into multiple CKs of a fixed size and organizes them into multiple CKGs. When a disk fails, the disks of the CKG where the CKs in the faulty disk reside also participate in reconstruction. This significantly increases the disks involved in the reconstruction, improving the data reconstruction speed. In addition, block virtualization distributes data to all the disks in a storage system and leverages the I/O processing capability of the storage system.

• Extent

  A block of a fixed size in a CKG, 4 MB by default. The extent is the smallest unit of a thick LUN, as well as the smallest unit used to calculate the requested space, released space, and relocated data.

• Grain

  A small block of a fixed size divided from extents. The default size of a grain is 64 KB. When all the disks in a storage pool are Solid State Drives (SSDs), the default size of a grain is 8 KB. Grains are basic units that constitute a thin LUN.

• Hot spare space

  Space used for data reconstruction of faulty blocks in block virtualization. When a CK is faulty, the system lets a CK of the hot spare space take over and instructs the other CKs in the CKG to perform data reconstruction using the hot spare space. This ensures data integrity and read/write performance.

• Reconstruction
  A process of restoring the data saved on a faulty disk to hot spare CKs and replacing the CKs on the faulty disk with the hot spare CKs. During data reconstruction, valid data and parity data must be read and processed to restore the data saved on a faulty disk to hot spare space, thereby ensuring data security and reliability. Traditional reconstruction technologies allow only all disks in the same RAID group as the faulty disk to participate in reconstruction. The RAID 2.0+ technology enables all disks of the same type and in the same disk domain as the faulty disk to participate in reconstruction, boosting data reconstruction speed and shortening the time needed to recover the data.

  Data on other disks will be read for reconstruction. Therefore, to prevent reconstruction failures, service interruption, and data loss, do not remove other disks of the same type as the faulty disk in the disk domain where the faulty disk resides during reconstruction.