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About tiering policies

Tiering policy

The tiering policy function is used to assign a specific storage tier to a specific DP-VOL. A tiering policy specifies subset of tiers that is available to a given set of DP-VOLs.

Tier relocation changes the location of previously stored data. It is performed in conformance to the tiering policy. If a DP-VOL is initially allocated to a low-speed tier and the tiering policy is changed to a high-speed tier, relocation is performed in the next cycle.

For example, if you set the tiering policy level on a V-VOL (DP-VOL) to a tier with a high I/O speed, the data is always stored on the high-speed tier when relocating tiers. When you use that V-VOL (DP-VOL), regardless of the actual size of the I/O load, you can always get high-speed responses. See Tiering policy levels.

When you create the DP-VOL, you can designate one of six existing tiering policies and define up to 26 new tiering policies. See Tiering policy levels and Setting tiering policy on a DP-VOL.

Use the Edit LDEVs window to change the tiering policy settings. When tier relocation occurs, the related tiering policy set for the DP-VOL is used to relocate data to the desired tier or tiers.

The tiering policy does not own pool capacity. Rather, pool capacity is shared among tiers. Pages are allocated in order of priority from upper to lower tiers in a tiering policy. When you specify a new allocation tier, pages are allocated starting from the tier that you specify.

The tier range, frequency distribution, and used capacity are displayed per tiering policy: existing tier level All(0), Level1(1) through Level5(5), and Level6(6) to Level31(31).

Custom policies

The settings of the tiering policy can be changed and these tiering policies changed by a user are called custom policies. Custom policies can be defined for IDs of tiering policies from 6 to 31 (from Level6(6) to Level31(31)). The following items can be set in the custom policy:

  • Rename custom policy
  • Change allocation threshold
Custom policy name

A custom policy name can be changed arbitrarily. You can change the names of custom policies from Level6(6) to Level31(31). For example, if you change the name of Level6(6) to Policy06, Policy06(6) will then be displayed.

Allocation threshold

You can define allocation thresholds in new policies from Level6(6) to Level31(31).

For all DP-VOLs that have the tiering policy in a pool, Dynamic Tiering performs the relocation of pages to each tier based on the tiering policy setting.

Max(%) and Min(%) parameters: When a tiering policy is created, 4 types of parameters can be set: Tier1 Max and Tier 1 Min, Tier 3 Max and Tier 3 Min. Each parameter setting is a ratio that corresponds to the total capacity of the allocated area of DP-VOLs that have the same tiering policy set for a pool.

Tier1 and Tier3 parameter settings can also limit the capacity for all volumes in a configuration that contain multiple DP-VOLs that have the same intended use. These settings can prevent conditions such as the following from occurring:

  • Excess allocation of SSD capacity for unimportant applications.
  • Degradation in average response time for high performance operations.

Tiering policy examples

The following figure shows the allocation threshold settings Tier1 Max=40%, Tier1 Min=20%, Tier3 Max=40%, and Tier3 Min=20% for a DP-VOL with a Level6(6) setting when the initial mapped capacity is 100GB.

GUID-4208E1B4-AF40-45DA-BC18-CEB509856619-low.png

The following figure shows an example of data allocation when the default tiering policy level All(0) is specified. Pages in the DP-VOL are relocated to any tier.

GUID-9A5FDD0C-478C-4384-8900-A13536BFB53F-low.gif

The following figure shows an example of data allocation when setting the tiering policy to Level1(1) (see Level1(1) in Tiering policy levels). In this case, pages in the DP-VOL are relocated to tier 1, and are not relocated to other tiers.

GUID-D443703A-5DFA-4D02-990D-90D7D1962BAD-low.png

Setting tiering policy on a DP-VOL

The setting of a tiering policy for a DP-VOL is optional. If one is not selected, the default is the All(0) tiering policy level. The available levels are listed in Tiering policy levels. DP-VOLs of different tiering policies can coexist in one pool. If you specify the level of the tiering policy, DP-VOLs with the policy are grouped together.

  • All(0) is the default policy. In this case, data is stored to all of the tiers.
  • When a tier is added to the pool after setting the tiering policy on a DP-VOL, the DP-VOL is relocated according to the new tier lineup.

    For example, if you set the tiering policy to level 5, the data is always allocated to the tier of the low I/O speed. If the pool has two tiers, data is stored in tier 2. If a new tier is added, the number of tiers becomes three and if the new tier is the lowest tier, relocation will be performed to move data into tier 3.

For more information about tiering policy and groups, see Tiering policy levels.

Tiering policy levels

Tiering policy

1 tier pool

2 tier pool

3 tier pool

Note

All(0)

Single Tier

Both tiers

All 3 tiers

Default Tiering Policy

Level1(1)

Same as All(0)

Tier 1

Tier 1

Data is located to the Top Tier. Any overflow moves to the next lower tier.

Level2(2)

Same as All(0)

Same as All(0)

Tier 1 and Tier 2

See note

Data is located to the Top Tier after Level1(1) assignments are processed. Any overflow moves to the next lower tier.

Level3(3)

Same as All(0)

Same as All(0)

Tier 2

See note

Data is located to the Middle Tier. Any overflow moves to the top tier.

Level4(4)

Same as All(0)

Same as All(0)

Tier 2 and Tier 3

See note

Data is located to the Middle Tier after Level3(3) assignments are processed. Any overflow moves to the next lower tier.

Level5(5)

Same as All(0)

Tier 2

Tier 3

See note

Data is located to the bottom tier. Any overflow moves to the next higher tier.

From Level6(6) to Level31(31)

Same as All(0)

Depends on user setting

Depends on user setting

For example:

If additional capacity is added to the pool and the capacity defines a new Tier 1 or new Tier 2, the DP-VOLs with a Level 5(5) assignment will not physically move but Level 5(5) will be associated with Tier 3.

If additional capacity is added to the pool and the capacity defines a new Tier 3, the DP-VOLs with a Level 5(5) assignment will physically move to the new Tier 3 and Level 5(5) will be associated with Tier 3.

Reserving tier capacity when setting a tiering policy

If you set the tiering policy of a DP-VOL, the DP-VOL used capacity and the I/O performance limitation are reserved from the tier. The reserved limit performance per page is calculated as follows:

The reserved limit performance per page = (The performance limit of the tier) ÷ (The number of pages in the tier).

A DP-VOL without a tiering policy setting uses the unreserved area in the pool.

GUID-8643FCCB-90A8-427C-B858-2E2426E94EE1-low.png

Example of reserving tier capacity

The reservation priority depends on the level of tiering policy. The following figure illustrates the reservation priority. Tiers are reserved in order of priority from (1) to (7) in the figure. If the pool-VOL capacity is deficient when you reserve a tier, the nearest tier of your specified tier is allocated. If you specify two tiers like level 2 or level 4 of the tiering policy, first of all the upper tier is reserved. At this time, if the capacity of the pool-VOL assigned to the upper tier is deficient, the lower tier defined by the tiering policy is reserved automatically. For example, in case of level 2 in the diagram below, tier 1 is reserved first. If the capacity of tier 1 is deficient at this point, tier 2 is reserved automatically. For details, see Notes on tiering policy settings.

Tier reservation priority

Tiering policy

Reserved tier

1

Level1(1)

Tier 1

2

Level3(3)

Tier 2

3

Level5(5)

Tier 3

From 4 to 29

From Level6(6) to Level31(31)

The custom policy whose number is small is prioritized.

Tier 1: From Level6(6) to Level31(31), each of the Tier1 Min values are reserved.

Tier 2: From Level6(6) to Level31(31), each of values that deducted the total value of Tier1 Max and Tier3 Max from 100(%) are reserved.

Tier 3: From Level6(6) to Level31(31), each of the Tier3 Min values are reserved.

30

All(0)

All tiers

Level2(2)

Tier 1 and Tier 2

Level4(4)

Tier 2 and Tier 3

From Level6(6) to Level31(31)

Tier 1: From Level6(6) to Level31(31), each of the Tier1 Max values are reserved.

Tier 3: From Level6(6) to Level31(31), each of the Tier3 Max values are reserved.

GUID-85897019-E551-4598-B376-3EA8A3A4FE89-low.png

Notes on tiering policy settings

  • If Auto is set as the execution mode, tier relocation is performed based on the monitoring cycle. Therefore, when the tiering policy setting is changed, tier relocation will automatically implement the tiering policy at the end of the current monitoring cycle. See Example 1 in Execution mode settings and tiering policy.
  • If Manual is set as the execution mode, you must manually perform monitoring, issue a monitor stop, and then start relocation (see Example 2, Case 1, in Execution mode settings and tiering policy). If you change the tiering policy settings while obtaining monitoring data, the monitoring data is used for the next tier relocation (see Example 2, Case 2, in Execution mode settings and tiering policy). Therefore, you do not need to perform new monitoring.
  • If a capacity shortage exists in the tier being set, a message may appear in the View Tier Property window that the page allocation cannot be completed according to the tiering policy specified for the V-VOL. Should that occur, the page allocation in the entire pool, including the tier that defines the tiering policy might not be optimized.
    NoteThe message that page allocation cannot be completed according to the tiering policy does not appear when these tiering policies are set:
    • All(0)
    • In a 2-tier configuration, Level2(2), Level3(3), or Level4(4) which is equivalent to All(0)

    When a capacity shortage exists in a tier, you can revise the setting of the tiering policy or the configuration of tiers. If the capacity of one tier is fully exhausted, the migrating pages are assigned to the next tier according to the tiering policy.

    • Level1(1): When tier 1 is full, the remaining pages are allocated to tier 2. If tier 2 is full, the remaining pages are allocated to tier 3.
    • Level3(3): When tier 2 is full, the remaining pages are allocated to tier 1. If tier 1 is full, the remaining pages are allocated to tier 3.
    • Level5(5): When tier 3 is full, the remaining pages are allocated to tier 2. If tier 2 is full, the remaining pages are allocated to tier 1.
    • Level2(2), Level4(4), and from Level6(6) to Level31(31): When the specified tier is full, the unallocated pages are kept in the prior tier or they are allocated to the tier that has free space. From Level 6 (6) to Level 31 (31), the names of tiering policies can be changed. If these names have changed, the new names appear.
  • If a performance shortage exists in the tier being set, pages may not be allocated in conformance to the tiering policy specified for the V-VOL. In that case, pages are allocated according to the performance ratio of each tier.

    As shown in the following table, allocation capacity considerations are based on the tiering policy.

    Tiering Policy

    Allocation capacity considerations

    All(0), Level2(2), or Level4(4)

    Tier range and I/O performance

    Level1(1), Level3(3), or Level5(5)

    Tier range

    From Level6(6) to Level31(31)

    First phase: Tier range.

    Allocation capacities in each tier.

    • Tier1: The setting value(%) in Tier1 Min.
    • Tier2: The value deducted Tier1 Max(%) and Tier3 Max(%) from 100(%).
    • Tier3: The setting value(%) in Tier3 Min.

    Second phase: Tier range and I/O performance.

    Capacities deducted from the mapped capacities of the first phase from the total used capacity, are mapped to each tier.

Execution mode settings and tiering policy

The following figure depicts how tier relocation is performed after changing the tiering policy setting while Auto execution mode is used.

GUID-C24EF963-A915-486D-95CB-5ED5256D1B95-low.png

The following figure depicts two cases of how tier relocation is performed after changing the tiering policy setting while Manual execution mode is used.

GUID-BD4A7A60-56F7-4947-BAC3-FB994954D277-low.png

New page assignment tier

If you set the new page assignment tier value, when a new page is needed by a DP-VOL the page is taken from the specified tier aligned with the new page assignment tier value. You can set this function by using Hitachi Device Manager - Storage Navigator. In addition, this function becomes effective just after setting. The following table lists setting values:

Setting value

Description

High

The new page is assigned from the higher tier of tiers set in the tiering policy.

Middle

The new page is assigned from the middle tier of tiers set in the tiering policy.

Low

The new page is assigned from the lower tier of tiers set in the tiering policy.

The following tables show the tiers to which new pages are preferentially assigned.

Tiering Policy

When specifying High

When specifying Middle

When specifying Low

Note

All

From tier 1 to 2

From tier 1 to 2

From tier 2 to 1

If you set Low, tier 2 is given a priority over tier 1.

Level 1

From tier 1 to 2

From tier 1 to 2

From tier 1 to 2

Assignment sequences when High, Middle, and Low are same.

Level 2

From tier 1 to 2

From tier 1 to 2

From tier 2 to 1

Every assignment sequence is the same as when All is specified as the tiering policy.

Level 3

From tier 1 to 2

From tier 1 to 2

From tier 2 to 1

Every assignment sequence is the same as when All is specified as the tiering policy.

Level 4

From tier 1 to 2

From tier 1 to 2

From tier 2 to 1

Every assignment sequence is the same as when All is specified as the tiering policy.

Level 5

From tier 2 to 1

From tier 2 to 1

From tier 2 to 1

Assignment sequences when High, Middle, and Low are same.

Number

Condition

Order of new page allocation

1

T1 MIN = 100%

Same as Level1(1)

2

T1 MAX = 0%

Same as Level5(5)

3

T1 MAX > 0%

Same as All(0)

Tiering policy

When specifying High

When specifying Middle

When specifying Low

Note

All

From tier 1, 2, to 3.

From tier 2, 3, to 1.

From tier 3, 2, to 1.

Specifying High, Middle or Low to the assignment sequence is effective.

Level 1

From tier 1, 2, to 3.

From tier 1, 2, to 3.

From tier 1, 2, to 3.

Assignment sequences when High, Middle, and Low are same.

Level 2

From tier 1, 2, to 3.

From tier 1, 2, to 3.

From tier 2, 1, to 3.

If you set Low, tier 2 is given a priority over tier 1.

Level 3

From tier 2, 3, to 1

From tier 2, 3, to 1

From the 2, 3, to 1

Assignment sequences when High, Middle, and Low are same.

Level 4

From tier 2, 3, to 1

From tier 2, 3, to 1

From tier 3, 2, to 1

If you set Low, tier 3 is given priority over tier 2.

Level 5

From tier 3, 2, to 1

From tier 3, 2, to 1

From tier 3, 2, to 1

Assignment sequences when High, Middle, and Low are same.

Number

Condition

Order of new page allocation

1

T1 MIN = 100%

Same as Level1(1)

2

T3 MIN = 100%

Same as Level5(5)

3

T1 MAX > 0% and T3 MAX = 0%

Same as Level2(2)

4

T1 MAX = 0% and T3 MAX = 0%

Same as Level3(3)

5

T1 MAX = 0% and T3 MAX > 0%

Same as Level4(4)

6

T1 MAX > 0% and T3 MAX > 0%

Same as All(0)

Relocation priority

If you use the relocation priority function, you can set the selection priority of a DP-VOL when performing relocation. With this setting, a prioritized DP-VOL can be relocated earlier during a relocation cycle. You can set this function by using Hitachi Device Manager - Storage Navigator. The function is activated after the monitoring data is collected.

  • If no relocation priority is set for all DP-VOLs, the general order of DP-VOL selection is to select the next DP-VOL in LDEV number order after the last DP-VOL that fully performed relocation. This selection order persists across relocation cycles.
  • If one or more DP-VOLs is assigned a relocation priority, the prioritized DP-VOLs are operated upon in the early portion of the relocation cycle, before others in the general order of DP-VOL selection.
  • If V-VOL is not given priority for relocation:

    For example, if LDEVs of LDEV IDs with LDEV#1, LDEV#2, LDEV#3, LDEV#4, and LDEV#5 are not given priority for relocation, LDEVs are relocated with the following sequences. In this example, three LDEVs are relocated in each period, but the number of LDEVs to relocate may change by the relocation cycle or the data size.

    Relocating cycle

    Relocating sequence of LDEV#1 in each cycle

    Relocating sequence of LDEV#2 in each cycle

    Relocating sequence of LDEV#3 in each cycle

    Relocating sequence of LDEV#4 in each cycle

    Relocating sequence of LDEV#5 in each cycle

    T1

    1st

    2nd

    3rd

    Unperformed

    Unperformed

    T2

    3rd

    Unperformed

    Unperformed

    1st

    2nd

    T3

    Unperformed

    1st

    2nd

    3rd

    Unperformed

    T4

    2nd

    3rd

    Unperformed

    Unperformed

    1st

  • If V-VOL is given priority for relocation:

    For example, if LDEVs of LDEV IDs with LDEV#3 and LDEV#4 are set priority for relocation from LDEV#1 to LDEV#5, LDEVs are relocated with the following sequences. In this example, three LDEVs are relocated in each period, but the number of LDEVs to relocate may change by the relocation cycle or data size.

    Relocating cycle

    Relocating sequence of LDEV#1 in each cycle

    Relocating sequence of LDEV#2 in each cycle

    Relocating sequence of LDEV#3 in each cycle

    Relocating sequence of LDEV#4 in each cycle

    Relocating sequence of LDEV#5 in each cycle

    T1

    3rd

    Unperformed

    1st

    2nd

    Unperformed

    T2

    Unperformed

    3rd

    1st

    2nd

    Unperformed

    T3

    Unperformed

    Unperformed

    1st

    2nd

    3rd

    T4

    3rd

    Unperformed

    1st

    2nd

    Unperformed

Assignment tier when pool-VOLs are deleted

When you delete pool-VOLs, the pages allocated to the pool-VOLs are moved to other pool-VOLs. The following table shows the tier numbers to which pages are allocated before and after pool-VOLs are deleted. This operation does not depend on the tiering policy or the settings of newly assigned tiers. Relocate tiers after deleting pool-VOLs.

The following table describes page allocation in a 3-tier configuration.

Tier of deleted pool-VOLs

Order in which pages are allocated to tiers

Description

Tier 1

Tier 1, Tier 2, and Tier 3

If there is free space in Tier 1, pages are allocated to Tier 1.

If there is no free space in Tier 1, pages are allocated to Tier 2.

If there is no free space in Tier 1 and Tier 2, pages are allocated to Tier 3.

Tier 2

Tier 2, Tier 1, and Tier 3

If there is free space in Tier 2, the pages are allocated to Tier 2.

If there is no free space in Tier 2, pages are allocated to Tier 1.

If there is no free space in Tier 1 and Tier 2, pages are allocated to Tier 3.

Tier 3

Tier 3, Tier 2, and Tier 1

If there is free space in Tier 3, pages are allocated to Tier 3.

If there is no free space in Tier 3, pages are allocated to Tier 2.

If there is no free space in Tier 2 and Tier 3, pages are allocated to Tier 1.

The following table describes page allocation in a 2-tier configuration.

Tier of deleted pool-VOLs

Order in which pages are allocated to tiers

Description

Tier 1

Tier 1 and Tier 2

If there is free space in Tier 1, pages are allocated to Tier 1.

If there is no free space in Tier 1, pages are allocated to Tier 2.

Tier 2

Tier 2 and Tier 1

If there is free space in Tier 2, pages are allocated to Tier 2.

If there is no free space in Tier 2, pages are allocated to Tier 1.

 

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