Planning Disk Domains
A disk domain provides storage space for storage pools, whose storage available capacities depend on the capacity and hot spare policy of the disk domain. The capacity of the disk domain and hot spare policies must be properly planned to ensure full utilization of storage space.
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
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 3-3 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 |
Number of Disks of Which Capacity Is Used as Hot Spare Space in a High Hot Spare Policya |
Number of Disks of Which Capacity Is Used as Hot Spare Space in a Low Hot Spare Policya |
|---|---|---|
(1, 12] |
1 |
1 |
(12, 25] |
2 |
|
(25, 125]b |
3 |
2 |
(125, 325] |
4 |
|
…… |
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a: Huawei storage systems use RAID 2.0+ virtualization technology. Hot spare capacity is provided by member disks in each disk domain. Therefore, the hot spare capacity is expressed in the number of disks in this table. For example, if a disk domain is composed of 12 SSDs and the high hot spare policy is used, the hot spare space occupies the capacity of one SSD and the capacity is provided by member disks in the disk domain. If a disk domain is composed of 13 SSDs and the high hot spare policy is used, the hot spare space occupies the capacity of two SSDs. b: When the number of disks at a storage tier reaches 125, the storage tier uses the capacity of one disk in every 200 additional disks as the hot spare space in a high hot spare policy. |
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- 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.
- 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.
Table 3-4 describes the best practices for disk domain planning in video surveillance scenarios.
Planning Rule |
Example |
|---|---|
The maximum number of disks in a disk domain is 72. If possible, evenly allocate disks to each disk domain. A disk domain is cost-effective when it contains 72 disks.
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In the scenario to store data of 840 video channels at the bit rate of 4 Mbit/s for 30 days, 4 TB disk enclosures and a total of 352 disks are required. You are advised to configure the back-end SAS loops as follows:
Recommended disk domain division:
Disk allocation:
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The evaluation results of the local Huawei representative office or Huawei authorized distributor supersede the considerations in this section.