About tiering policies

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.

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.

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.

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.

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.

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.

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.

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.

• 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.

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

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

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:

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

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

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.

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

Create pools