Volume Migration requires resources (differential tables and pair tables) for execution.
Differential tables and pair tables are resources shared with Volume Migration and ShadowImage. Note that you cannot concurrently run Volume Migration for pairs more than half of the number of system volumes in the storage system. If you want to increase the dedicated shared memory, contact customer support.
Note that you cannot increase shared memory for VSP One B24.
The following table shows the numbers of differential tables and pair tables for VSP One B24.
|
Added shared memory (Shared memory function) |
Number of differential tables |
Number of pair tables |
|---|---|---|
|
Base (No shared memories are added.) |
419,200 |
32,768 |
The following table shows the numbers of differential tables and pair tables for VSP One B26.
|
Added shared memory (Shared memory function) |
Number of differential tables |
Number of pair tables |
|---|---|---|
|
Base (No shared memories are added.) |
419,200 |
32,768 |
|
Extension1 |
419,200 |
32,768 |
The following table shows the numbers of differential tables and pair tables for VSP One B28.
|
Added shared memory (Shared memory function) |
Number of differential tables |
Number of pair tables |
|---|---|---|
|
Base (No shared memories are added.) |
419,200 |
32,768 |
|
Extension1 |
419,200 |
32,768 |
|
Extension2 |
419,200 |
32,768 |
The numbers of differential tables and pair tables that are required for Volume Migration execution depend on the capacity of the volume to be migrated.
The following describes how to calculate the numbers of differential tables and pair tables that are required for migration of a volume.
Note that that following calculation is not necessary when you use a Dynamic Provisioning virtual volume whose capacity exceeds 4 TB because such a volume does not use differential tables.
Number-of-differential-tables-required-for-migration-of-a-volume
＝ ↑((Capacity-of-the-volume*1(KB)) ÷ 256) ÷ (Nmmber-of-slot-that-can-be-managed-by-one-differential-table*2(20,448))↑
Number-of-pair-tables-required-for-migration-of-a-volume
＝ ↑ Number-of-differential-tables-required-for-migration-of-a-volume ÷ 36 ↑
↑: Indicates that the resulting value of the part enclosed by this sign is to be rounded up to the nearest whole number.
*1: The capacity of the volume after split if a volume is split by the VLL function
*2: For details about the number of slots, see the VSP One Block Provisioning Guide.
The maximum number of pairs for which Volume Migration can be concurrently run in a storage system can be calculated as Z when all the following three conditions (A to C) are satisfied:
A. Total number of differential tables used for VM execution ≦ Number of remaining differential tables
Σ((Number-of-differential-tables-required-for-migration-of-a-volume) * Number-of-VMs (Za))
≦ Maximum-number-of-differential-tables-for-the-storage-system - Number-of-differential-tables-in-use
B. Total number of pair tables used for VM execution ≦ Number of remaining pair tables
Σ((Number-of-pair-tables-required-for-migration-of-a-volume) * Number-of-VMs (Zb))
≦ Maximum-number-of-pair-tables-for-individual-storage-systems – Number-of-pair-talbes-in-use
C. The smaller value between the total number of VMs executed in A and the total number of VMs executed in B
Z = min(ΣZa,ΣZb)
For details about how to calculate the numbers of differential tables and pair tables that are used by a software product other than Volume Migration, see the manual for the applicable software product.
Example calculation
Conditions:
- Storage system model: VSP One B28
- Capacity of the volume: 3,019,898,880 KB
- Number of differential tables in use: 360,000
- Number of pair tables in use: 10,000
Number-of-differential-tables-required-for-migration-of-a-volume
＝ ↑(3,019,898,880 ÷ 256) ÷ 20,448↑ ＝ ↑576.9014085↑ ＝ 577
Number-of-pair-tables-required-for-migration-of-a-volume
＝ ↑577 ÷ 36 ↑ ＝ ↑16.0277778↑ ＝ 17
577 * Za ≦ 419,200 - 360,000 ＝ 59,200
The maximum value of Za that satisfies the above equation is 102.
17 * Zb ≦ 32,768 - 10,000 ＝ 22,768
The maximum value of Zb that satisfies the above equation is 1339.
Therefore, the maximum number of pairs for which Volume Migration can be concurrently run in a storage system is 102.