Planning Disk Domains

Planning Disk Types for a Disk Domain

Disks can be classified into SSDs, SAS disks, and NL-SAS disks.

A disk type in a disk domain corresponds to a storage tier in a storage pool. If the disk domain does not have a specific disk type, the corresponding storage tier cannot be created for a storage pool.

Table 4-3 describes the mapping between disk types and storage tiers.

Planning Hot Spare Policies for a Disk Domain

To prevent data loss or performance deterioration caused by a member disk failure, a storage system uses hot spare space to take over data from the failed member disk. The following hot spare policies are supported:

• High

  The capacity of one disk is used as hot spare space if the number of disks at a storage tier is equal to or fewer than 12. The hot spare space non-linearly increases as the number of disks increases.

• Low

  The capacity of one disk is used as hot spare space if the number of disks at a storage tier is equal to or fewer than 25. The hot spare space non-linearly increases as the number of disks increases.

  Number of disks of which capacity is used as hot spare space in a low hot spare policy = Number of disks of which capacity is used as hot spare space in a high hot spare policy/2 (rounded up)

• None (not supported by 18000 or 18000F series storage systems)

  The storage system does not provide any hot spare space. In the event a member disk in a disk domain fails, the storage system uses the free capacity in the disk domain for reconstruction. If the free capacity in the disk domain is insufficient, the storage system uses the unallocated capacity in storage pools for reconstruction. If reconstruction fails, the disk domain will change to the Degrade state, which will cause the read/write performance to deteriorate, affecting the storage system reliability.

Table 4-4 describes how hot spare space changes for a single engine with the number of disks. The hot spare space changes at a storage tier are used as an example here. The hot spare space changes at different storage tiers are the same.

• Number of Disks in the above tables refers to the number of same-type disks owned by a same engine. If you select disks from multiple engines to create a disk domain, calculate the number of disks used for hot spare space on each engine and sum up the values.
• For 18000 and 18000F series storage systems, the high hot spare policy is used by default. You are not allowed to modify the hot spare policy on DeviceManager. To modify the hot spare policy, run the change disk_domain general command in the CLI.

• When you are creating a disk domain, ensure that the disks used to provide hot spare space are sufficient.
• Hot spare space can be used for a specific disk domain only.
• Common capacity changes of the hot spare space are listed in this section. The number of disks supported by a storage system and the capacity of hot spare space are based on actual specifications.

Recommended Configurations for Disks in a Disk Domain

You are advised to configure a maximum of 100 disks for each tier in a disk domain. For example, if the number of disks on a tier is D (divide D by 100 and then round off the result to N and the remainder is M), you can refer to the following configurations:

• If D ≤ 100, configure all disks on this tier in one disk domain.
• If D > 100, create N+1 disk domains and evenly distribute all disks to the N+1 disk domains. That is, the number of disks in each disk domain is D/(N+1). In addition, it is recommended that disk enclosures be fully configured.
• For SmartTier, it is recommended that a maximum of 100 disks be configured for each tier in a disk domain. The configuration of disks on each tier also follows the preceding principle.

Example 1: The total number of SSDs in a storage system is 328, which is the value of D. (Divide 328 by 100. Round off the result to 3, which is the value of N. The remainder is 28, which is the value of M). You are advised to configure four disk domains, each of which contains 328/4 = 82 SSDs.

Example 2: The total number of SSDs in a storage system is 223, which is the value of D. (Divide 223 by 100. Round off the result to 2, which is the value of N. The remainder is 23, which is the value of M). You are advised to configure three disk domains, each of which contains 223/3 = 74.3 disks. In this case, two disk domains are configured with 74 disks respectively and the other disk domain is configured with 75 disks.

Example 3: If a disk domain consists of SSDs, SAS disks, and NL-SAS disks, for SmartTier, the number of disks of each type cannot exceed 100.

If a project requires a disk domain containing over 100 disks to meet capacity and service planning requirements, contact Huawei technical support engineers for evaluation.

Planning Capacity for a Disk Domain (OceanStor 5000, 5000F, 6000, and 6000F Series Storage Systems)

The space of a storage pool originates from a disk domain. Therefore, the capacity of the disk domain determines the available capacity of the storage pool. When planning the minimum capacity for a disk domain, you must set related parameters including the hot spare policy, RAID policy, and storage media to ensure that the disk domain can meet capacity requirements. Table 4-5 describes the minimum number of disks required for a disk domain (for a single engine).

• The previous table only lists the minimum number of disks required in standard RAID levels. The storage system also supports flexible configuration. For a flexibly configured RAID policy xD+yP, the minimum disk number is x + y + z when the number of required hot spare disks is z. The z value is determined by the hot spare policy and disk quantity.
• The disks listed in the Minimum Number of Disks in a Disk Domain column of the preceding table must be provided by the same engine. If the disks that you use to create a disk domain are provided by different engines, ensure that the number of disks on each engine meets the disk number requirements (minimum number of disks).
• Under Specify disk type in the Create Disk Domain window, you can select the following three types of disks: High-Performance tier: SSD, Performance tier: SAS, and Capacity tier: NL-SAS. If you select only one type, at least four disks of this type are required for each engine. If you select two or three types of disks, at least two SSDs, four SAS disks, and four NL-SAS disks are required for each engine.
• RAID 0 can only be configured using the CLI. For details, see the command reference specific to your product model and version.

Planning Capacity for a Disk Domain (OceanStor 18000 and 18000F Series Storage Systems)

The space of a storage pool originates from a disk domain. Therefore, the capacity of the disk domain determines the available capacity of the storage pool. When planning the minimum capacity for a disk domain, you must set related parameters including the hot spare policy, RAID policy, and storage media to ensure that the disk domain can meet capacity requirements. Table 4-6 describes the minimum number of disks required for a disk domain (for a single engine).

• The previous table only lists the minimum number of disks required in standard RAID levels. The storage system also supports flexible configuration. For a flexibly configured RAID policy xD+yP, the minimum disk number is x + y + z when the number of required hot spare disks is z. The z value is determined by the hot spare policy and disk quantity.
• The disks listed in the Minimum Number of Disks in a Disk Domain column of the preceding table must be provided by the same engine. If the disks that you use to create a disk domain are provided by different engines, ensure that the number of disks on each engine meets the disk number requirements (minimum number of disks).
• Under Specify disk type in the Create Disk Domain window, you can select the following three types of disks: High-Performance tier: SSD, Performance tier: SAS, and Capacity tier: NL-SAS. If you select only High-Performance tier: SSD, at least six disks of this type are required for each engine. If you select only Performance tier: SAS or Capacity tier: NL-SAS, at least eight disks of this type are required for each engine. If you select two or three types of disks, at least six SSDs, eight SAS disks, and eight NL-SAS disks are required for each engine.
• RAID 0 can only be configured using the CLI. For details, see the command reference specific to your product model and version.

Suggestions

Refer to the following suggestions to plan disk domains:

• When creating a disk domain, manually select disks to ensure that all disks are from the same engine. Create disk domains on one engine to reduce the probability of disk failure and improve the read and write performance of disks.
• You are advised to use disks of the same type, capacity, and rotating speed (except SSDs) in the same storage tier in a disk domain. If disk capacities are not the same, disks with large capacities may not be used effectively. If disk rotating speeds are different, performance may deteriorate.
• You are advised to create different disk domains for the block and file storage services. If you want to configure both block and file storage services in one disk domain, contact Huawei technical support engineers to help you evaluate the practicality.
• To ensure that a storage pool meets the recommended data reliability requirements, you are advised to properly plan the number of disks at a single storage tier in a disk domain. For details, see "Planning Whether to Use the Enhanced RAID Data Protection Policy" in "Planning Storage Pools".