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StorageTek SL3000 Systems Assurance Guide E20876-08 |
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# A Best Practices

This appendix provides best practices and fundamentals of operation for the SL3000 library to optimize library performance. The key practices include library configuration planning, content management, partitioning, and networking.

## Library Configuration Planning

When selecting modules and features of the SL3000 library, there are fundamental guidelines that should be followed to maximize library performance. This section describes best practices to optimize library performance when adding expansion modules, dual robotics, cartridge access ports, and tape drives.

### Cartridge Expansion Module

The initial CEM should be installed to the right of a Base, then a second to the left of the drive expansion module, a third to the right, and the fourth one to the left, and so on. This alternating method provides the best usage of the cartridge slots.

A balance of CEMs—to the left and to the right—provides for the most efficient operation. Cartridge expansion modules can be installed with up to four to the right and up to four to the left. Installing four CEMS only on one side increases the amount of robotic travel, resulting in a decrease of overall library performance.

### Parking Expansion Module

The inaccessible arrays in a PEM do not need to be removed. This allows the customer to restore this module to a CEM at anytime. However, any data cartridges in the inaccessible arrays cannot be accessed by the client.

### Access Expansion Module

When entering and ejecting cartridges in smaller quantities, use the smaller rotational CAPs to complete the job. These CAPs are easier to use and take less time to audit than the larger AEM bulk load CAPs.

### Robotic Rails and TallBots

The robotic units in an SL3000 library are called TallBots. Each library can have either one (standard) or two (redundant) TallBots that are driven along two extrusions, called rails, on the rear wall of the library.

Rails are continuous and allow the TallBots to travel the length of the library from end-to-end. However, in a dual TallBot configuration, there is a robotic safety zone that prevents collisions. When using redundant TallBots, Access or Parking Expansion Modules must be installed at both ends of the library string.

- Parking Expansion Modules (PEMs) have an area of inaccessible cartridge slots in the event of a TallBot failure. The defective TallBot either moves into or is pushed into this area while the other—redundant—TallBot continues library operations.

- Access Expansion Modules provide an area or "garage" where the defective TallBot is parked. A service representative can then replace this TallBot without interrupting library operations.

Using redundant TallBots for content management offers:

- Increased speed for library operations—two robotic units working in parallel

- Redundant operations should one unit fail

### Cartridge Access Ports

When planning the workloads, place applications that require significant enters and ejects adjacent to the CAP magazines.

CAP control is split down the centerline. Make sure there is a left- and right-side CAP to support the library. If a CAP encounters a failure, all CAPs to the outside of the failed CAP, will be unusable until the defective CAP is serviced. Therefore, install CAPs in a balanced fashion around the centerline.

- If a redundant CAP is required and no DEM is installed, install the CEM with a CAP on the left. If a DEM is installed, then place the CEM on the right and install a CAP on the DEM.

If partitioning, the recommendation is to install enough CAPs to provide at least one CAP for each partition. This allows each partition to contain a dedicated CAP. CAPs can be shared between similar hosts. For example, FC SCSI hosts can share CAP resources and HLI hosts can share those resources (CAPs).

Place labels outside on the library wall indicating which CAP and which magazine gets what type of cartridge. Labels are provided for the customer to identify the cartridge access ports.

Insert cartridges with the correct orientation:

- Fully seated and laying flat within the slots

- Parallel to the floor, hub-side down

- Barcode label pointing out and below the readable characters.

### Tape Drives

During the installation, logically grouping tape drives can improve performance. Strategies to use when determining where to install the tape drives include:

- Install tape drives that use the same media types closer to those slots. For example, place T9840 drives on the left side of the drive bay with their cartridges to the left and LTO drives on the right side with their matching media to the right.

- Install enough tape drives to adequately handle peak workloads.

- Configure heavy tape applications so they do not exceed the performance limits of the library configuration.

- Use a tool such as QuickLine or a Tape Library Configurator to determine the optimal drive configurations.

- In a dual-robotics library, performance can be improved by separating drives with a blank column down the center of the drive arrays.

## Content Management

Proper content management can maximize the performance of the library. When planning for content it is important to consider the best way to manage cartridges, effects of adding active capacity, and the effects of partitioning.

### Managing Cartridges

Managing cartridges in the library can have an affect on performance. Use a library management application such as LCM with ELS to keep active volumes and compatible drives closer together and to migrate less active volumes farther away from the drives. Use the watch_vols utility for ACSLS.

Use a float option to help with performance. When float is on, the management software can automatically select a new home slot for a cartridge on a dismount. Make sure the library contains enough free slots to allow the selection of a new home slot during the dismount.

Cluster frequently used cartridges close together and as near to the tape drives as possible. Group or partition the cartridges by workload with enough tape drives to support the maximum, peak activity.

Enter cartridges through the CAP.

- When manually placing cartridges in the library with the front door open, library operations cease and the library management software must perform a full audit to update the library database to match the actual contents.

- When entering cartridges through the CAP, the library stays online so that mounts can continue and the library automatically updates the database.

Eject cartridges efficiently. There are two ways (host functions) to eject cartridges: ordered and unordered.

- When the host specifies an ordered eject, the library places the cartridges in a specific sequence. This operation is significantly slower than unordered ejects. Ordered ejects are used for vaulting, which simplifies the external operations.

- When the host specifies an unordered eject, the library ejects cartridges as it can, often in a random order.

Manage the available space in the library:

- Plan for times of peak activity.

- Keep an adequate supply of scratch cartridges in the library.

- Move inactive cartridges out of the library to ensure there is adequate space for active cartridges.

### Capacity on Demand

Capacity on Demand is a non-disruptive optional feature that allows the customer to add active capacity to the libraries.

#### Non-disruptive Capacity Changes

Changes to active capacity result in minimal disruptions to library operations. The specific library behavior depends on the type of host connection, HLI or FC-SCSI.

Note: Although changes to active capacity are not disruptive to library hosts, it is recommended that you make the library unavailable to other users before committing the active storage region changes.

You can increase active capacity without stopping host jobs or having host connections go offline. When you decrease capacity, the library goes offline only momentarily and then comes back online automatically.

With FC-SCSI libraries, whenever you make any of the following changes, the library goes offline temporarily with a Unit Attention condition:

- Activate or deactivate a storage cell.

- Add, change, or remove a host connection.

- Remove an empty drive slot.

Multiple error messages may be generated, and all hosts must issue the appropriate commands to update their library configuration information. See the appropriate tape management software documentation for detailed procedures and commands. In the case of adding or removing drives, the device SCSI numbering is updated as well.

### Partitioning

The benefits of a partitioned library include:

- More than one operating system and application managing the library

- An improvement in the protection or isolation of files

- An increase in system and library performance

- An increase in user efficiency

Partitions allow for a customized fit, such as:

- Giving multiple departments, organizations, and companies access to the resources of the library

- Isolating clients at service centers

- Separating different encryption key groups

- Dedicating partitions for special tasks

Partitions are defined by assigning rectangular boundaries. Currently the SL3000 supports up to 60 rectangular boundaries per partition within the library.

Any slots added to a partition are considered active. Therefore, adding to a partition increases the total number of active slots in the library. Ensure that the library has enough active capacity when adding to a partition. If more active capacity is required, purchase additional activation permits.

Note: If a partition contains slots that are being displaced because an optional CAP is being installed, the customer must remove all these slots from any partition definitions before shutting down the library. Failure to do this will result in a service call and engineering assistance to recover partition definitions.

#### Non-Disruptive Partitioning

The non-disruptive partitioning (NDP) feature minimizes the number of host interruptions that occur when partitions are modified. The library does not need to be taken offline for every partition change. Hosts that are not connected to the changed partition are not disrupted.

The specific functions of the NDP feature vary, depending on the type of host-partition connection. For details, refer to the SL3000 User's Guide.

#### Rectangular Boundaries

Rectangular boundaries provide the customer with a resource to better optimize cartridge placement within the library. To do this, the customer selects boundaries within the library by using the same method as defining a partition. This rectangular boundary can be just one or two slots, a row, a column, or an entire module.

Available slots use the same numbering scheme of the library within the boundaries—starting in the upper left, then counting to the lower right—for the activated capacity of the library. The figures that follow provide an example of partitioning with rectangular boundaries. The figures are simplified and do not represent the actual physical layout of the library.

The Figure A-1 below shows a sample library where the customer has defined:

- Two selected partitions (A and B)

- Four Rectangular boundaries called AR1, BR1, BR2, and BR3

- A library activated for 50 slots: AR1-1 through 20, BR1-1 through 8, BR2-9 through 28, and BR3-29 through 30

Figure A-1 Adding Capacity to Partitions - Adding 50 Slots

In Figure A-2 below, the customer has added five more slots to partition A by creating two more rectangular boundaries: AR2 and AR3.

- AR2 slots 21-24 and AR3 slots 25

Because there are no more slots under AR2-24, the customer must go to the right and create a boundary for the fifth slot AR3-25, an example of a single slot rectangular boundary.

Figure A-2 Adding Capacity to Partitions - Adding 5 More Slots

In Figure A-3 below, the customer has added 12 more slots to partition A.

- AR2 slots 21-28 and AR3 slots 29-32

Because there are no more slots to the right of AR2-28, the customer must go to another area of the library with installed, yet inactive, slots to continue with the addition. To do this, the boundary AR3 was created to the left of boundary AR1.

Figure A-3 Adding Capacity to Partitions - Adding 12 More Slots

#### Guidelines for Partitioning

The SL3000 library can support up to eight partitions using a variety of interface types: only Ethernet partitions, only SCSI partitions, or combinations of both.

Essential guidelines for understanding partitions are:

- Clear communication between the system programmers, network administrators, library software representatives and administrators, and service representatives.

- Customers must be current on maintenance levels of their library management software.

- A clearly written and drawn out plan for partitioning must be completed and agreed upon by all partition members.

- One partition will not recognize another partition within the library. Other partitions are either not reported or marked as inaccessible.

- CAPs may be allocated to one or more partitions. However:

  - Sharing a CAP between HLI and SCSI partitions is not permitted.

  - CAP sharing among SCSI partitions is not recommended.

- Since CAPs can be either shared or dedicated among partitions:

  - Automatic mode for shared CAP operations is not supported.

  - Automatic mode for dedicated CAP operations is supported.

- If a host has a CAP reserved for enter or eject operations for a partition, no other hosts or partitions can have access to the CAP.

  The SL3000 library has an optional feature to add cartridge access ports to the drive expansion and cartridge expansion modules for a total of up to 10 rotational CAPs.

  Note: For SCSI hosts, automatic CAP mode is supported for one partition at a time if the shared CAP is associated with that partition. A shared CAP that has been associated with a partition acts as a dedicated CAP until the association changes.

- Duplicate VOLSERs are supported by the library; however, the library management software may not support this unless the duplicate VOLSERs are in different partitions.

  - With ELS/HCS-managed partitions, the duplicate VOLSERs must be in different control data sets.

  - With ACSLS-managed partitions, the duplicate VOLSERs must be on different ACSLS servers.

#### Planning the Data Path for Partitions

When planning for partitions, you also need to be aware of the location, quantity, type, and need for the tape drives and media.

Likewise, a clear understanding about how to logically group and install the tape drives and locate media for the different hosts, control data sets, and interface types is necessary.

When planing for partitions:

- Make sure the tape drive interface supports that operating system.

  - Open system platforms do not support ESCON or FICON interfaces.

  - Not all mainframes support Fibre Channel or LTO tape drives.

- Make sure the media types match the application.

- Install tape drives that use the same media types in the same partition.

#### Host Software Precautions when Partitioning

When you partition or re-partition a library, you do not have to reboot or IPL the library. However, when you remove resources from a partition, the library will take the affected partition offline temporarily. For this reason, it is best to minimize any disruptions to the operating systems and library management software before you partition.

The amount of time the affected partition goes offline is minimal, from 10 to 15 seconds, unless work is in the queue. The library will wait for queued jobs to complete before taking the partition offline. This action affects only the changed partition, not the entire library. Anytime resources are removed from a partition, the change is disruptive only to the host(s) connected to the altered partition.

An example of a procedure that all hosts (ACSLS or ELS/HSC) should follow when partitioning or changing partitions is:

1. Plan the distribution of cartridges, such as enters, ejects, and moves.

2. Use the remote SLC software to change the partitioning configuration.

3. The host(s) will get a configuration change message, and should audit the library with the host software to update the accessible cartridges and storage slots in the host software's database. SCSI hosts will need to re-learn the library if anything has changed on their partition.

#### Partitioning in the Performance Zone

The performance zone is an area within the SL3000 library that is closest to the tape drives. Because of the physical location, volumes in this zone have faster access and response times to the tape drives.

Selection of the volumes that reside in this zone is critical to obtain the best performance. Volumes that benefit the most from the performance zone are:

- Applications such as VSM, HSM, and ABARS

- Volumes that tend to be recalled regularly

- Most recently created volumes

- Volumes that need fast access time

- Volumes that require very few ejects

Volumes that do not meet any of the above criteria should be moved out of this area. Once this zone is full, volumes would extend into the regular storage area.

## Networking

Whenever possible, use a dedicated, secure private network for communication between the library and host management software. A secure private network connection using an Ethernet hub or switch is required for maximum throughput and minimum resource contention.

If a shared network is used or required by the customer, these actions can help with the communication between the host and the library:

- Directly connect the library to a switch.

- Place the library on its own subnet.

- Use a managed switch that can:

  - Set priorities on ports to give the host and library higher priority.

  - Provide dedicated bandwidth between the host and the library.

  - Create a VLAN between the host and the library.

Use a virtual private network (VPN) to insulate host to library traffic.

## Using World Wide Names

The SL3000 library assigns World Wide Name (WWN) addresses to drives. The WWN does not change when the drive is swapped or replaced and host parameters do not need to be changed or re-configured.

Normally, blocks of World Wide Name (WWN) addresses are assigned to manufacturers by the IEEE Standards Committee and are built into devices during manufacture. In the case of the SL3000 Tape Library, however, the library assigns World Wide Node Names and World Wide Port Names to the drives. This technique is referred to as "library-centric world wide names." Potential drive slots are each assigned a WWN which does not change when a drive is swapped or replaced.

In the SL3000 library, a WWN for a drive is implemented through an algorithm that uses the frame serial number of the library and the drive's position within the library. Only the last two digits change within the library. The second-to-the-last digit represents the frame number (starting at 0 for Frame 1) and the last digit is the drive row (starting at 1). The WWN of the drive is location-dependent and not device-dependent. That is, each time a drive is reset or turned on, the library re-establishes the WWN so that a drive in frame x, row y always retains the same WWN—host parameters do not need to be changed or re-configured. The library's configuration can also easily survive a reboot. The following sections describe methods that involve World Wide Names in resolving these issues.

### Tape Drive Dynamic World Wide Name

Each connection (port) in a Fibre Channel environment must have a unique ID called the World Wide Name (WWN). The WWN is a 64-bit address that identifies each individual device.

When a tape drive logs-in to a Fibre Channel network, the WWN is validated for access by comparing Port Name, Node Name, and Port ID. All three of these identifiers must match or this indicates the configuration has changed and the port is blocked from access.

The dynamic World Wide Name (dWWN) feature assigns world wide names to the library drive slots rather than the drives themselves. This allows you to swap or replace devices, such as tape drives, without bringing down the entire operating system.

### Using Persistent Binding

When a server is booted, devices are discovered and assigned SCSI target and LUN IDs. It is possible for these SCSI assignments to change between boots. Some operating systems do not guarantee that devices will always be allocated the same SCSI target ID after rebooting. Also, some software depends on this association, so you do not want it to change. The issue of SCSI ID assignment is addressed by persistent binding.

Persistent binding is a host bus adapter (HBA) function that allows a subset of discovered targets to be bound between a server and device.

Implemented by a World Wide Node Name (WWNN) or World Wide Port Name (WWPN), persistent binding causes a tape drive's World Wide Name to be bound to a specific SCSI target ID.

After a configuration has been set, it survives reboots and any hardware configuration changes because the information is preserved. If a drive needs to be replaced, the new drive assumes the WWNN of the old drive because the WWNN for the drive is location-dependent within the library. Because the WWNN does not change, persistent binding does not need to be changed, which would otherwise cause an outage.

### Using Zoning to Isolate Devices and Enhance Security

For security reasons, it is important to limit the devices that a server or servers can recognize or access. Also, some performance configurations and Storage Area Network (SAN) configurations can result in a device being seen multiple times from the same server. For example, if you have two host bus adapters (HBAs) from the same server connected to a tape drive in the SL3000 Tape Library, the drive will be detected and appear as two logical devices. That is, there will be two special files for one physical device. Zoning can address these issues.

Zoning allows you to partition your SAN into logical groupings of devices so that each group is isolated from the other and can only access the devices in its own group. Two types of zoning exist: hardware zoning and software zoning. Hardware zoning is based on physical fabric port number. Software zoning is defined with the World Wide Node Name (WWNN) or World Wide Port Name (WWPN).

While zoning can be re-configured without causing an outage, some zoning configurations can become complicated. The advantage of the library's WWNN implementation is that you can avoid the exposure of introducing zoning errors because there is no need to change the zoning configuration if a drive needs service or replacement.