Physical

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Use this section to determine the number of physical volumes that are required to accommodate the workload you are planning for the TS7770 Tape Attach and the TS7760 Tape Attach.

To determine the number of physical volumes that are required to accommodate your workload, consider: If you use the Copy Export function, plan for the additional physical volumes taken offsite.

Number of virtual volumes

Because in most instances the data on a virtual volume is stored on a physical volume, the number of virtual volumes has a direct effect on the number of physical volumes required.

On the TS7720 tape attach or the TS7760 tape attach, virtual volumes in partition CP0 are not stored in physical volumes. Virtual volumes in other partitions are stored in physical volumes.

On the TS7740, all virtual volumes are stored in physical volumes.

Average amount of data on a volume

The TS7700 stores only the amount of data you write to a virtual volume plus a small amount of metadata.

Amount of data stored for a given host workload

The amount of data that is stored per workload can be extracted from your Tape Management System, such as RMM, or from TS7700 by using VEHSTATS.

Average compression ratio achieved per workload

The data that a host writes to a virtual volume might be compressible. The space that is required on a physical volume is calculated after the effect of compression. If you do not know the average number for your data, assume a conservative 2:1 ratio.

Average utilization rate of filling physical volumes

The average utilization rate of filling physical volumes can be calculated from the Reclaim Threshold Percentage. The percentage that is used to determine when to perform reclamation of free storage on a stacked volume. When the amount of active data on a physical stacked volume drops below this percentage, a reclaim operation is performed on the stacked volume. The valid range of possible values is 0 - 95%; 35% is the default value. Therefore, the utilization rate of filling physical volumes should range from 35% to 100%. The average utilization rate of filling physical volumes can be calculated as (35+100)/2 = 67.5%.

Selective Dual Copy function

If you use this function for some or all your data, a virtual volume can be written to a second physical volume, in addition to the first physical volume, resulting in two physical volumes in the same physical library.

Copy Export

The Copy Export function creates a disaster recovery solution by allowing physical volumes that contain a copy of selected virtual volumes to be ejected from the TS7700 and moved to an offsite location. If you use this function, plan for the number of additional physical volumes that are required and whether you want to use a specific VOLSER for them. The default number of managed, exported physical volumes is 2,000. However, this value can be adjusted to a maximum of 10,000 using the Copy Export Settings panel of the TS7700 Management Interface.The TS7700 limits the number of exported physical volumes that it manages at any time to a maximum of 2,000. This is to ensure that the physical volumes offsite would not exceed the slot capacity of a TS3500 Tape Library.
Note: Attachment to a TS3500 Tape Library via a 3953 L05 Library Manager is only supported by TS7740 microcode levels prior to 8.5.0.xx. Attachment to a TS3500 Tape Library without a 3953 L05 Library Manager is supported by TS7740 microcode level 8.5.0.xx or later.

Delete Expired Volume Data setting

If an Expire Time is not set for a virtual volume's scratch category, virtual volumes occupy space on the physical volumes even after they were returned to scratch. In that case, only when a virtual volume is rewritten is the old data released to reduce the amount of active data on the physical volume. When the scratch category Expire Time is set, the data that is associated with volumes that were returned to scratch are deleted after Reclamation is run. For example, assume that you have 20,000 virtual volumes in scratch status at any point in time and that the average amount of data on a virtual volume is 400 MB and that the data compresses at a 2:1 ratio. The space that is occupied by the data on those scratch volumes is 4,000,000 MBs or the equivalent of 14 3592 JA cartridges. By using the scratch category Expire Time, you can reduce the number of cartridges required in this example by 14.

Secure Data Erasure

Secure Data Erasure monitors the age of expired data on a physical volume and forces a reclaim and physical overwrite of the data on the volume when its age exceeds a limit set by you.

Secure Data Erasure also accounts for whether a volume was encrypted. If a volume was not encrypted or only a portion of it was encrypted, the non-encrypted area of the volume is erased by loading it on a drive and having the drive perform a Data Security Erase operation. If all of the data area on a volume was encrypted, then instead of performing the Data Security Erase operation, the volume is loaded on a drive and the externally encrypted data key is erased from the media, rendering the data unrecoverable. This reduces the amount of time to erase a volume from more than 2 hours to just a few minutes.

Reclaim threshold settings

The percentage used to determine when to perform reclamation of free storage on a stacked volume. When the amount of active data on a physical stacked volume drops below this percentage, a reclaim operation is performed on the stacked volume. The valid range of possible values is 0 - 95%; 35% is the default value. The number of required physical volumes also depends on the reclaim threshold percentage that you specified for the minimum amount of active data on a volume before it becomes eligible for reclamation. The reclaim threshold setting can have a large impact on the number of physical volumes required. Physical volumes hold between the threshold value and 100% of data. Having too low a setting results in the need for more physical volumes, and having too high a setting can affect the TS7700's ability to perform host workload because it is using its resources to perform reclamation. Experiment to find a threshold that matches your needs.

Scratch physical volumes

You should plan for at least 10 scratch physical volumes to be available in the common media pool. If dedicated pools are used with the borrow/return sharing disabled, at least 10 scratch physical volumes per dedicated pool should be added.You should refer the following diagram to determine the number of scratch physical volumes you need for each pool.
  1. Is the 60F, 60G, E08 or E07 drive installed?
    • Yes
      1. Is borrow/return sharing enabled?
        • Yes: 15 volumes in the common scratch pool
        • No: 15 volumes in each dedicated pool
    • No
      1. Is borrow/return sharing enabled?
        • Yes: 50 volumes in the common scratch pool
        • No: 50 volumes in each dedicated pool
If the number of scratch physical volumes in your system is fewer than these thresholds:
  • Reclamation of sunset media does not occur
  • Reclamation runs more frequently
You can have less than 15 or 50 volumes in your pool if these conditions are acceptable. Keep in mind that you need at least 2 scratch physical volumes to avoid an out of scratch state.

Number of physical volume pools

For each physical volume pool, plan to use at least three scratch physical volumes. These are in addition to the number of physical volumes that are calculated to hold the data on the virtual volumes.
The following is a suggested formula to calculate the number of physical volumes needed:
Where:
Pv = Total number of physical volumes needed
Da = Total amount of data that is returned from your Tape Management System
or VEHSTATS per workload
Cr = Compression Ratio per workload
  (Use Cr=1 when Da represents previously compressed data)
Ut = Average utilization rate of filling physical volumes
Pc = Capacity of a physical volume in TB
Px = Resulting number of physical volumes needed for a particular workload "x"
Ps = Number of physical volumes in common scratch pool

For each workload, calculate the number of physical volumes needed:
Px = (Da/Cr)/(Pc × Ut/100)

Next, add in physical scratch counts and the Px results from all known workloads:
Pv = Ps + P1 + P2 + P3 + ...

For example, by using the following assumptions:
Workload 1
Da
Cr
Ut
Pc
=
=
=
=
100 TB
2
67.5%
10 TB (capacity of a JD volume)
P1 = (100/2)/(10 × 67.5/100) = 8 physical volumes
Workload 2
Da
Cr
Ut
Pc
=
=
=
=
150 TB
2
67.5%
7 TB (capacity of a JC volume in 3592-E08 format)
P2 = (150/2)/(7 × 67.5/100) = 16 physical volumes

If the number of physical volumes in the common scratch pool is Ps = 15, you would need to plan on the following number of physical volumes in the TS7770 Tape Attach or the TS7760 Tape Attach:

Pv = Ps + P1 + P2 = 15 + 8 + 16 = 39 physical volumes

If you need dual copied virtual volumes, you need to double the number of physical volumes for that workload. If a workload uses dedicated pools with the borrow/return sharing disabled, then each workload must have its own dedicated additional scratch count versus the shared Ps count.