Tier relocation rules, restrictions, and guidelines

Rules

Performance monitoring, using both Auto and Manual execution modes, observes the pages that were allocated to DP-VOLs prior to the start of the monitoring cycle and the new pages allocated during the monitoring cycle. Pages that are not allocated during performance monitoring are not candidates for tier relocation.

Tier relocation can be performed concurrently on up to eight pools. If more than eight pools are specified, relocation of the ninth pool starts after relocation of any of the first eight pools has completed.

If Auto execution mode is specified, performance monitoring may stop about one minute before to one minute after the beginning of the next monitor cycle start time.

The amount of relocation varies per cycle. In some cases, the cycle may end before all relocation can be handled. If tier relocation does not finish completely within the cycle, relocation to appropriate pages is executed in the next cycle.

Calculating the tier range values will be influenced by the capacity allocated to DP-VOLs with relocation disabled and the buffer reserve percentages.

While a pool-VOL is being deleted, tier relocation is not performed. After the pool-VOL deletion is completed, tier relocation starts.

Frequency distribution is unavailable when there is no data provided by performance monitoring.

While the frequency distribution graph is being created or the tier range values are being calculated, the frequency distribution graph is not available. The time required for determining the tier range values varies depending on the number of DP-VOLs and total capacity. The maximum time is about 20 minutes.

To balance the usage levels of all parity groups, rebalancing may be performed after several tier relocation operations. If rebalancing is in progress, the next cycle of tier relocation might be delayed.

For details on rebalancing, see Rebalancing the usage level among parity groups.

Performance monitoring or tier relocation conditions

The status of data collection, fixed monitoring, and tier relocation operations are described in the following table. The latest fixed monitoring information is referenced when tiers are relocated.


Monitoring information or execution conditions	Status of data collection in progress	Status of fixed monitoring information used in tier relocation	Tier relocation operations	Solutions
Unallocated pages.	Pages are not monitored.	No monitoring information on pages.	Tiers of the pages are not relocated.	Unnecessary. After the pages are allocated, monitoring and relocation are performed automatically.
Zero data is discarded during data monitoring.	Monitoring on pages is reset.	Only monitoring information on pages is invalid.	Tiers of the pages are not relocated.	Unnecessary. After the pages are allocated, monitoring and relocation are performed automatically.
V-VOL settings do not allow tier relocation.	Volume is monitored.	Monitoring information on the volume is valid.	If the tier relocation setting is being disabled at the performance monitoring finish time, tiers of the volume are not relocated.	N/A
When V-VOLs are deleted	Volume is not monitored.	Only monitoring information on the volume is invalid.	Tier relocation of the volume is suspended.	N/A
When execution mode is changed to `Manual` from `Auto` or vice versa.	Suspended.	Monitoring information collected before suspension is valid.	Suspended.	Collect the monitoring information again if necessary.¹
When the power switch is power ON or OFF.	Monitoring is suspended by powering OFF and is not resumed even after powering ON.¹	Monitoring information collected during the previous cycle is continuously valid.	Tier relocation is suspended by powering OFF and is resumed after powering ON.	Collect the monitoring information again if necessary.¹
When Volume Migration is performed. When Quick Restore of ShadowImage is performed.	The monitoring information of the volume is not collected at the present moment. In the next monitoring period, the monitoring information will be collected.	Monitoring information is invalid and the volumes need to be monitored.	Tier relocation to volumes is suspended.	Collect the monitoring information again if necessary.¹
S-VOL of the following products when the initial copy operation is performed: TrueCopy Global-active device Universal Replicator	Monitoring information is collected continuously, but the monitoring of the volumes is reset.²	No effect on the fixed monitoring information. The monitoring information collected during the previous cycle continues to be valid.	Tier relocation to volumes is suspended.	Collect the monitoring information again if necessary.¹
When the number of tiers increases by adding pool-VOLs. When the pool-VOLs of the tiers are switched by adding pool-VOLs.³ When tier rank of the external LDEV is changed.	Continued.	Fixed monitoring information is invalid because the monitoring information was discarded. If monitoring is set to the continuous mode, weighted data calculated by using the monitoring information in past periods is also discarded.	Suspended.	Relocate tiers again.¹
When pool-VOLs are deleted.	Continued.	Monitoring information is invalid temporarily. The monitoring information is calculated again after deleting of pool-VOLs.⁴	Deleting the pool-VOL stops the tier relocation. The process resumes after the pool-VOL is deleted.	N/A
When a cache is blocked.	Continued.	No effect on the fixed monitoring information. The monitoring information collected during the previous cycle continues to be valid.	Suspended.	After recovering the faulty area, relocate tiers again.¹
When an LDEV is blocked. (Pool-VOL or V-VOL)	Continued.	No effect on the fixed monitoring information. The monitoring information collected during the previous cycle continues to be valid.	Suspended.	After recovering the faulty area, relocate tiers again.¹
When the depletion threshold of the pool is nearly exceeded during relocation.	Continued.	No effect on the fixed monitoring information. The monitoring information collected during the previous cycle continues to be valid.	Suspended.	Add pool-VOLs, then collect monitoring information and relocate tiers again.¹
When execution mode is `Auto` and the execution cycle ends during tier relocation.	At the end time of execution cycle, data monitoring stops.	The monitoring information collected before monitoring performance stops is valid.	Suspended.	Unnecessary. The relocation is performed automatically in the next cycle.
When execution mode is `Manual` and 7 days elapse after monitoring starts.	Suspended.	The monitoring information collected before suspension is valid.	Continued.	Collect the monitoring information again if necessary.¹
Notes: The execution mode is Auto or the script is written in manual execution mode, information is monitored again and tiers are relocated automatically. All pages of the S-VOLs are not allocated, and the monitoring information of the volume is reset. After the page is allocated to the new page, the monitoring information is collected. Example: Pool-VOLs of SAS15K are added to the following Configuration 1 Configuration 1 (before change): Tier 1 is SSD, Tier 2 is SAS10K, and Tier 3 is SAS7.2K. Configuration 2 (after change): Tier 1 is SSD, Tier 2 is SAS15K, and Tier 3 is SAS10K and SAS7.2K. The monitoring information status is changed from invalid (INV) to calculating (PND). After completion of calculating, the monitor information status is changed from calculating (PND) to valid (VAL).