TSM tape storage pools

Tape storage pools are typically used within TSM for both primary and copy storage pools. Tape is an ideal medium for backup and archive data storage because of its cost/MB ratio, ease of transporting offsite and high read/write performance. Tape devices are defined to TSM via library and drive definitions.

Each physical library (of whatever tape technology) is associated with or mapped to a tape device class definition. The device class definition informs TSM about the type of drive being used - for example, format and capacity. Tape drives within a large tape library can be logically grouped to meet performance requirements for different groups of data.

6.4.1 Tape device performance considerations

Different tape technologies have performance characteristics, which can be quantitatively related to RTO requirements for any given volume of data. To meet RTO performance requirements for management classes, tape libraries are sized and assigned to tape storage pools. This mapping enables TSM to know the device characteristics of the storage pool media, and how to access it when data is written to or accessed from a storage pool. Figure 6-7 illustrates the fundamental reasoning behind designing tape storage pools to meet recovery time objectives for different classes of data.

Figure 6-7 Relating RTO, management classes and device classes.

As shown in Figure 6-7, tape drive performance can be estimated in terms of individual and aggregate throughput. Performance benchmarks for

uncompressed data I/O are available from tape drive technology vendors. If multiple drives are installed in a library, the aggregate throughput capacity can be calculated and directly compared to RTO requirements for data volume versus time, as shown in Table 6-1.

Table 6-1 The basic tape drive aggregate performance equation

These measurements assume perfect performance - that is, they do not take account of tape seek and mount time, the number of volumes required for a set of data, and the physical distribution of data across one or multiple volumes.

Since these variables are unpredictable, it is difficult to quantitatively factor them into preliminary real-world tape library performance estimates. Therefore, it is advised to reduce specified performance rates, say by 20% Once a TSM

Drive I/O # of Drives Aggregate I/O RTO (GB/Hr).

15 MB/s 4 216 GB/Hr. 190

Volumes Volumes Volumes Volumes Volumes Volumes

Tape Library

TapeStorage Pool/ Library A:

60 MB/s Throughput Collocation / Reclamation On/Off Tape Library Partition A:

4 TB Volume Capacity Tape Media Type A

Tape Storage Pool/Library B:

30 MB/s Throughput

Disk Storage Pool Tape Storage Pool and Library A Tape Storage Pool and Library B Management Class A

Management Class B

Management Class C

environment is running in a live customer environment with real data, more accurate performance measurements and sizing metrics can be developed.

Collocation and reclamation settings also significantly impact tape restore performance, and must be taken into consideration for each tape storage pool definition. For each storage pool and associated management class data, these variables must be carefully considered for restore performance. 7.11.1,

“Collocation considerations for offsite vaulting” on page 160 and 7.11.2,

“Reclamation considerations for offsite vaulting” on page 161 discuss these factors in greater detail.

6.4.2 Tape library sizing fundamentals

At an enterprise level, tape library sizing must take into consideration current backup and archive volume, data characteristics, and high level performance requirements. High level tape library sizing methods are discussed in Getting Started with Tivoli Storage Manager; Implementation Guide, SG24-5416. The same capacity planning methods can be applied at a lower level against specific groups of management classes and device classes as needed.

Another important element of tape library selection involves strategic planning for tape media and devices. Enterprise tape considerations should include:

򐂰 Tape library hardware strategy for technology, performance, and scalability

򐂰 Tape format/density and tape media road map

򐂰 Hardware compression (on or off)

򐂰 Software or TSM compression standards for client data

򐂰 Tape drive connectivity (SAN or SCSI)

For DR technical planning, we suggest the consolidation of tape resources into a single tape media and library format. Alternate site tape infrastructure must match production site tape infrastructure. Otherwise, the tape media type could become a risk to recovery operations. We recognize that many environments host a variety of tape and media types, however we stress the importance of strategic planning for DR capability and operational efficiencies. Mixed tape media types limit the functionality of collocation and reclamation, and can make offsite tape management procedures overly complex.

An important factor for tape media management is the volume per cartridge, which inevitably increases with time and innovation. If tape pools contain mixed capacity volumes, advanced tape management functions such as collocation or reclamation become less efficient. Currently, tape cartridge technology does not contain headerinformation to describe the cartridge capacity, so all tapes within a tape library are treated as volumetric equals. A principal way to control tape

volume efficiency is to allocate specific cartridge types to device classes and associated library partitions. New device classes with higher capacity cartridges can later be introduced. The migration process, or the MOVE NODEDATA or MOVE DATA commands can then be used to move data from one storage pool to another, where the storage pools use different device classes.

6.4.3 Versioning and tape storage pool sizing

The number and type of backup versions directly impacts tape storage pool sizing for capacity. Figure 6-8 illustrates a sample matrix which can be used to visualize and organize data volumes. Using this kind of matrix allows RTO requirements (through device class associations to storage pools), to be related to management classes, versioning policies, and the overall amount of volume required for each storage pool.

Figure 6-8 File versions, management class grouping, and storage pools

Once data is grouped by criticality into management classes, versioning and retention policies are applied. These policies impact directly the amount of storage volume required. Collectively, this overall volume of data must be known,

Management

Disk Storage Pool Tape Storage Pool A Tape Storage Pool B Tape Storage Pool C

Number of Versions

Storage Pool Type

in addition to growth forecasts, to accurately size the storage pools (both local and remote).