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Basic Storage Service Guide for File 15

OceanStor 5300 V3, 5500 V3, 5600 V3, 5800 V3, and 6800 V3 Storage System V300R003

"This document describes the basic storage services and explains how to configure and managebasic storage services."
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Huawei uses machine translation combined with human proofreading to translate this document to different languages in order to help you better understand the content of this document. Note: Even the most advanced machine translation cannot match the quality of professional translators. Huawei shall not bear any responsibility for translation accuracy and it is recommended that you refer to the English document (a link for which has been provided).
Planning the Capacity

Planning the Capacity

The capacity of a storage system is used to store service data and system data. To ensure that the capacity for service data is sufficient, plan the capacity for system data properly.

The capacity for storing system data refers to the file system capacity, hot spare capacity, and coffer disk capacity. The space overhead consumed by the storage system makes the actual available capacity smaller than the capacity provided by the storage system.

The space overhead consumed by the storage system comprises several parts:
  • Capacity used by parity data or mirrored data in a RAID group
    Table 2-1 lists the disk utilization of different RAID levels.
    Table 2-1  Disk utilization of different RAID levels

    RAID Level

    Disk Utilization

    RAID 0

    The disk utilization is 100%.

    RAID 1

    • 2Da: The disk utilization is about 50%.
    • 4D: The disk utilization is about 25%.

    RAID 3

    RAID 3 supports flexible configurations. Specifically, a RAID 3 policy allows data block and parity block policies ranging from 2D+1P to 13D+1P. The following examples show disk utilization rates of several configurations commonly used by RAID 3:
    • 4D + 1Pb: The disk utilization is about 80%.
    • 2D + 1P: The disk utilization is about 66.67%.
    • 8D + 1P: The disk utilization is about 88.89%.

    RAID 5

    RAID 5 supports flexible configurations. Specifically, a RAID 5 policy allows data block and parity block policies ranging from 2D+1P to 13D+1P. The following examples show disk utilization rates of several configurations commonly used by RAID 5:
    • 2D + 1P: The disk utilization is about 66.67%.
    • 4D + 1P: The disk utilization is about 80%.
    • 8D + 1P: The disk utilization is about 88.89%.

    RAID 6

    RAID 6 supports flexible configurations. Specifically, a RAID 6 policy allows data block and parity block policies ranging from 2D+2P to 26D+2P. The following examples show disk utilization rates of several configurations commonly used by RAID 6:
    • 2D + 2P: The disk utilization is about 50%.
    • 4D + 2P: The disk utilization is about 66.67%.
    • 8D + 2P: The disk utilization is about 80%.
    • 16D + 2P: The disk utilization is about 88.89%.

    RAID 10

    The disk utilization is 50%.

    RAID 50

    • (2D + 1P) x 2: The disk utilization is about 66.67%.
    • (4D + 1P) x 2: The disk utilization is about 80%.
    • (8D + 1P) x 2: The disk utilization is about 88.89%.

    a: D indicates the data block.

    b: P indicates the parity block.

    NOTE:

    For a flexibly configured RAID policy xD+yP, the disk utilization is [x/(x + y)] × 100%.

  • Capacity used by hot spare space
    To prevent data loss or performance deterioration caused by a member disk failure, the storage system employs hot spare space to take over data from the failed member disk.
    • If the product version is V300R003C00, 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 equals to or fewer than 12. The hot spare space non-linearly increases as the number of disks increases. When the number of disks at a storage tier reaches 168, the storage tier uses the capacity of one disk in every 96 disks as the hot spare space.

      • Low

        The capacity of one disk is used as hot spare space if the number of disks at a storage tier equals to or fewer than 24. The hot spare space non-linearly increases as the number of disks increases. When the number of disks at a storage tier reaches 168, the storage tier uses the capacity of one disk in every 192 disks as the hot spare space.

      • None

        The system does not provide hot spare space.

      Table 2-2 describes how hot spare space changes 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 types of storage tiers are the same.
      Table 2-2  Changes of hot spare space

      Number of Disks

      Number of Disks of Which Capacity Is Used as Hot Spare Space in High Hot Spare Policya

      Number of Disks of Which Capacity Is Used as Hot Spare Space in Low Hot Spare Policya

      (1, 12]

      1

      1

      (12, 24]

      2

      (24, 48]

      3

      2

      (48, 72]

      4

      (72, 120]

      5

      3

      (120, 168]

      6

      (168, 264]

      7

      4

      (264, 360]

      8

      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 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.

      NOTE:
      • 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 the current disk domain only.
      • Table 2-2 lists common capacity changes of the hot spare space. The number of disks supported by a storage system and the capacity of their hot spare space are based on actual specifications.
    • If the product version is V300R003C10 or V300R003C20, 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 equals to or fewer than 12. The hot spare space non-linearly increases as the number of disks increases. When the number of disks at a storage tier reaches 175, the storage tier uses the capacity of one disk in every 100 disks as the hot spare space.

      • Low

        The capacity of one disk is used as hot spare space if the number of disks at a storage tier equals to or fewer than 25. The hot spare space non-linearly increases as the number of disks increases. When the number of disks at a storage tier reaches 175, the storage tier uses the capacity of one disk in every 200 disks as the hot spare space.

      • None

        The system does not provide hot spare space.

      Table 2-3 describes how hot spare space changes 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 types of storage tiers are the same.
      Table 2-3  Changes of hot spare space

      Number of Disks

      Number of Disks of Which Capacity Is Used as Hot Spare Space in High Hot Spare Policya

      Number of Disks of Which Capacity Is Used as Hot Spare Space in Low Hot Spare Policya

      (1, 12]

      1

      1

      (12, 25]

      2

      (25, 50]

      3

      2

      (50, 75]

      4

      (75, 125]

      5

      3

      (125, 175]

      6

      (175, 275]

      7

      4

      (275, 375]

      8

      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 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.

      NOTE:
      • 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 the current disk domain only.
      • Table 2-3 lists common capacity changes of the hot spare space. The number of disks supported by a storage system and the capacity of their hot spare space are based on actual specifications.
  • Capacity used by coffer disks

    Part of the coffer disk space can be used to store critical system data, including user configuration data and system logs. The rest of the coffer disk space can be used to store service data. For details about capacity used by coffer disks, see the "Coffer Disk" of the corresponding model and version in the Product Description.

  • Capacity used by file systems and volume management software on the application server

    File systems and volume management software of multiple types on the application server may occupy a portion of space in the storage system. The actually occupied capacities depend on the deployment of applications on the application server.

  • WriteHole capacity

    WriteHole is used to resolve inconsistent data stripe verification caused by certain operations before I/Os are delivered to disks. Each disk reserves a 256 MB space as WriteHole capacity.

  • Capacity used by system information.

    The system information occupies 577 MB per disk.

  • Metadata capacity

    Each disk reserves 0.6% of its total capacity as metadata capacity, and reserves 2% as metadata backup capacity.

  • Reserved space for improving system performance and disk balance

    Each disk reserves 1% of its total capacity to improve system performance and disk balance. When 1% of the disk total capacity is smaller than 2 GB, 2 GB of space is reserved.

  • Integrated capacity

    When disks are being formatted, if the size of a sector is 520 bytes, the sector uses 8 bytes to store parity data. If the size of a sector is 4160 bytes, the sector uses 64 bytes to store parity data. The integrated capacity usage is about 98.46% (512/520 or 4096/4160).

Without considering the hot spare capacity consumption, you can use the following formula to calculate RAID 2.0+ disk capacity usage: RAID 2.0+ disk capacity usage = [1 – Metadata space – (1 – Metadata space) x Metadata backup space] x (1 – Disk space reserved for load balancing) x Integrated capacity usage = [1 – 0.6% – (1 – 0.6%) × 2%] x (1 – 1%) x 98.46% ≈ 94.95%

The disk capacity defined by disk manufacturers is different from that calculated by operating systems. As a result, the nominal capacity of a disk is different from that displayed in the operating system.

  • Disk capacity defined by disk manufacturers: 1 GB = 1,000 MB, 1 MB = 1,000 KB, 1 KB = 1,000 bytes.
  • Disk capacity calculated by operating systems: 1 GB = 1,024 MB, 1 MB = 1,024 KB, 1 KB = 1,024 bytes.
NOTE:

The preceding formulas are for reference only. The disk capacity displayed on the DeviceManager prevails.

Available Capacity Calculation Method

The following uses an example to explain how to calculate the allowed expansion capacity. Three valid digits are retained after the decimal point.

Assume that forty-eight 600 GB SAS disks will be added to the storage system, including four coffer disks and the hot spare policy and RAID policy are configured to Low and RAID 6 (8D + 2P) respectively. The allowed expansion capacity is calculated as follows:
  1. 600 GB is the nominal capacity provided by the disk vendor. Use the following method to convert this capacity to one that can be identified by the storage system:

    600GB x 1000 x 1000 x 1000/1024/1024 = 572204.590MB

    Storage systems provide the DIF function for end-to-end data protection. This function takes 1% to 2% of storage space. The following uses 2% as an example.

    572204.590 MB x (1 – 2%) = 560760.500 MB

  2. Minus the WriteHole capacity:

    572204.590 MB – 256 MB = 571948.590 MB

  3. Minus the reserved production space:

    571948.590 MB – 577 MB = 571371.590 MB

  4. Minus the metadata capacity:

    571371.590 MB x (1 – 0.6%) = 567943.361 MB

    NOTE:
    The storage system reserves 0.6% of each disk's space as metadata space. It dynamically allocates metadata space as services increase. The actual services prevail. The following uses 0.6% as an example.
  5. Minus the metadata backup capacity:

    567943.361 MB x (1 – 2%) = 556584.494 MB

  6. Minus the reserved space for improving system performance and disk balance:

    556584.494 MB x (1 – 1%) = 551018.649 MB

  7. Minus the integrated capacity:

    551018.649 MB x 98.46%= 542532.962 MB

  8. Because the hot spare policy of the storage system is set to Low, capacity of two disks is used as hot spare space capacity. Therefore, the remaining capacity is as follows after the hot space capacity is deducted:

    542532.962 MB x (48 – 2) = 24956516.250 MB

    Equals to 24956516.250 MB/1024/1024 = 23.800 TB

  9. Minus the coffer data capacity:

    23.800 TB – 4 x 5 GB = 23.781 TB

    NOTE:
    As an example, the capacity of the coffer disks is calculated as 5 GB. For details about capacity used by coffer disks, see the "Coffer Disk" of the corresponding model and version in the Product Description.
  10. Because the RAID policy of the storage system is RAID 6 (8D + 2P), the disk utilization is 80%. Therefore, the allowed expansion capacity is:

    23.781 TB x 80% = 19.025 TB

In this example, the allowed expansion capacity is 19.025 TB.
NOTE:
The preceding available capacity is for reference only. The capacity displayed on the DeviceManager management page prevails.
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Updated: 2019-02-01

Document ID: EDOC1000084198

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