Example 6: Change an ILM policy
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If your data protection needs to be changed or you add new sites, you can create and activate a new ILM policy.
Before changing a policy, you must understand how changes in ILM placements can temporarily affect the overall performance of a StorageGRID system.
In this example, a new StorageGRID site has been added in an expansion, and a new active ILM policy needs to be implemented to store data at the new site. To implement a new active policy, first create a policy. Afterward, you must simulate and then activate the new policy.
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The following ILM rules and policy are only examples. There are many ways to configure ILM rules. Before activating a new policy, simulate it to confirm it will work as intended to protect content from loss. |
How changing an ILM policy affects performance
When you activate a new ILM policy, the performance of your StorageGRID system might be temporarily affected, especially if the placement instructions in the new policy require many existing objects to be moved to new locations.
When you activate a new ILM policy, StorageGRID uses it to manage all objects, including existing objects and newly ingested objects. Before activating a new ILM policy, review any changes to the placement of existing replicated and erasure-coded objects. Changing an existing object's location might result in temporary resource issues when the new placements are evaluated and implemented.
To ensure a new ILM policy does not affect the placement of existing replicated and erasure-coded objects, you can create an ILM rule with an ingest time filter. For example, Ingest time is on or after <date and time>, so that the new rule applies only to objects ingested on or after the date and time specified.
The types of ILM policy changes that can temporarily affect StorageGRID performance include the following:
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Applying a different erasure-coding profile to existing erasure-coded objects.
StorageGRID considers each erasure-coding profile to be unique and does not reuse erasure-coding fragments when a new profile is used. -
Changing the type of copies required for existing objects; for example, converting a large percentage of replicated objects to erasure-coded objects.
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Moving copies of existing objects to a completely different location; for example, moving a large number of objects to or from a Cloud Storage Pool or to or from a remote site.
Active ILM policy for example 6: Data protection at two sites
In this example, the active ILM policy was initially designed for a two-site StorageGRID system and uses two ILM rules.
In this ILM policy, objects belonging to Tenant A are protected by 2+1 erasure coding at a single site, while objects belonging to all other tenants are protected across two sites using 2-copy replication.
Rule 1: One-site erasure coding for Tenant A
| Rule definition | Example value |
|---|---|
Rule name |
One-Site Erasure Coding for Tenant A |
Tenant Account |
Tenant A |
Storage Pool |
Site 1 |
Placements |
2+1 erasure coding in Site 1 from day 0 to forever |
Rule 2: Two-site replication for other tenants
| Rule definition | Example value |
|---|---|
Rule name |
Two-Site Replication for Other Tenants |
Tenant Account |
Ignore |
Storage Pools |
Site 1 and Site 2 |
Placements |
Two replicated copies from day 0 to forever: one copy at Site 1 and one copy at Site 2. |
ILM policy for example 6: Data protection at three sites
In this example, the ILM policy is being replaced with a new policy for a three-site StorageGRID system.
After performing an expansion to add the new site, the grid administrator created two new storage pools: a storage pool for Site 3 and a storage pool containing all three sites (not the same as the All Storage Nodes default storage pool). Then, the administrator created two new ILM rules and a new ILM policy, which is designed to protect data at all three sites.
When this new ILM policy is activated, objects belonging to Tenant A will be protected by 2+1 erasure coding at three sites, while objects belonging to other tenants (and smaller objects belonging to Tenant A) will be protected across three sites using 3-copy replication.
Rule 1: Three-site erasure coding for Tenant A
| Rule definition | Example value |
|---|---|
Rule name |
Three-Site Erasure Coding for Tenant A |
Tenant Account |
Tenant A |
Storage Pool |
All 3 Sites (includes Site 1, Site 2, and Site 3) |
Placements |
2+1 erasure coding in All 3 Sites from day 0 to forever |
Rule 2: Three-site replication for other tenants
| Rule definition | Example value |
|---|---|
Rule name |
Three-Site Replication for Other Tenants |
Tenant Account |
Ignore |
Storage Pools |
Site 1, Site 2, and Site 3 |
Placements |
Three replicated copies from day 0 to forever: one copy at Site 1, one copy at Site 2, and one copy at Site 3. |
Activating the ILM policy for example 6
When you activate a new ILM policy, existing objects might be moved to new locations or new object copies might be created for existing objects, based on the placement instructions in any new or updated rules.
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Errors in an ILM policy can cause unrecoverable data loss. Carefully review and simulate the policy before activating it to confirm that it will work as intended. |
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When you activate a new ILM policy, StorageGRID uses it to manage all objects, including existing objects and newly ingested objects. Before activating a new ILM policy, review any changes to the placement of existing replicated and erasure-coded objects. Changing an existing object's location might result in temporary resource issues when the new placements are evaluated and implemented. |
What happens when erasure-coding instructions change
In the currently active ILM policy for this example, objects belonging to Tenant A are protected using 2+1 erasure coding at Site 1. In the new ILM policy, objects belonging to Tenant A will be protected using 2+1 erasure coding at Sites 1, 2, and 3.
When the new ILM policy is activated, the following ILM operations occur:
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New objects ingested by Tenant A are split into two data fragments and one parity fragment is added. Then, each of the three fragments is stored at a different site.
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The existing objects belonging to Tenant A are re-evaluated during the ongoing ILM scanning process. Because the ILM placement instructions use a new erasure-coding profile, entirely new erasure-coded fragments are created and distributed to the three sites.
The existing 2+1 fragments at Site 1 aren't reused. StorageGRID considers each erasure-coding profile to be unique and does not reuse erasure-coding fragments when a new profile is used.
What happens when replication instructions change
In the currently active ILM policy for this example, objects belonging to other tenants are protected using two replicated copies in storage pools at Sites 1 and 2. In the new ILM policy, objects belonging to other tenants will be protected using three replicated copies in storage pools at Sites 1, 2, and 3.
When the new ILM policy is activated, the following ILM operations occur:
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When any tenant other than Tenant A ingests a new object, StorageGRID creates three copies and saves one copy at each site.
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Existing objects belonging to these other tenants are re-evaluated during the ongoing ILM scanning process. Because the existing object copies at Site 1 and Site 2 continue to satisfy the replication requirements of the new ILM rule, StorageGRID only needs to create one new copy of the object for Site 3.
Performance impact of activating this policy
When the ILM policy in this example is activated, the overall performance of this StorageGRID system will be temporarily affected. Higher than normal levels of grid resources will be required to create new erasure-coded fragments for Tenant A's existing objects and new replicated copies at Site 3 for other tenants' existing objects.
As a result of the ILM policy change, client read and write requests might temporarily experience higher than normal latencies. Latencies will return to normal levels after the placement instructions are fully implemented across the grid.
To avoid resource issues when activating a new ILM policy, you can use the Ingest time advanced filter in any rule that might change the location of large numbers of existing objects. Set Ingest time to be greater than or equal to the approximate time when the new policy will go into effect to ensure that existing objects aren't moved unnecessarily.
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Contact technical support if you need to slow or increase the rate at which objects are processed after an ILM policy change. |