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A tape library is a library where media can be added, removed, and moved between multiple libraries. The term removable media is used to specify various types of removable media supported by Commvault^® software, including tape and USB disk drives, which can be moved between MediaAgents for data protection and recovery operations.

Tape libraries best practices:

• Configure the tape library cleaning method to use. Software cleaning (Commvault) or hardware cleaning (library) can be used, but not both. A choice must be made.
• Share the tape library if required.
• Create a barcode pattern for cleaning tapes and assign it to the Cleaning Media group.
• If using multiple scratch media groups, create scratch groups and barcode patterns to use.
• Validate drive speed (from the CommCell Console) and document for future reference.

Tape libraries are divided into the following components:

• Library – is the logical representation of a library within a CommCell^® environment. A library can be dedicated to a MediaAgent or shared between multiple MediaAgents. Sharing of removable media libraries can be static or dynamic depending on the library type and the network connection method between the MediaAgents and the library.
• Master drive pool – is a physical representation of drives of the same technology within a library. An example of master drive pools would be a tape library with different drive types like LTO4 and LTO5 drives within the same library.
• Drive pool – is used to logically divide drives within a library. The drives can then be assigned to protect different jobs.
• Scratch pool – is defined to manage scratch media, also referred to as spare media, which can then be assigned to different data protection jobs.
  • Custom scratch pools – can be defined and media can be assigned to each pool.
  • Custom barcode patterns – can be defined to automatically assign specific media to different scratch pools or media can manually be moved between scratch pools in the library.

Library Types

Commvault software supports the drives for tape libraries:

• Standalone
• Blind
• Dedicated
• Static Shared
• Dynamic Shared
• Virtual Tape Library (VTL)
• USB Devices

Standalone

A standalone tape drive has no robotic media changer and no internal storage slots. Multiple standalone drives controlled by the same MediaAgent can be pooled together to support multi-stream jobs or cascade of a single stream job without having to respond to media handling requests. Media used by a Standalone library can be pre-stamped or new, and will be prompted for, by backup or restore jobs as necessary.

Blind

A 'blind' library has no barcode reader and is supported by the Commvault^® software maintaining the map/inventory externally in the CommServe^® server metadata.

Dedicated

A static configuration where the drives and media changer are connected to only one MediaAgent.

Static Shared

A static configuration where the drives and media changer are connected to only one of several MediaAgent hosts.

Example: In a library with four tape drives, one MediaAgent may have control of the media changer and two drives within the library while another MediaAgent may have control over the other two tape drives. A drive connected to one MediaAgent host is not accessible from the other MediaAgent hosts. Should the MediaAgent component having media changer control fail, no further loading/unloading of media can occur until that MediaAgent is active again. Shared libraries in today's world of Storage Area Networks (SAN) are not common.

Dynamic Shared

In a Dynamic Shared Library, the library drives and media changer are on a SAN and can be accessed by multiple MediaAgent hosts. Drives not being used by one MediaAgent can be assigned to and used by another MediaAgent. If the MediaAgent with control of the media changer fails, the control can be automatically passed to another MediaAgent. The primary advantage of a Dynamic Drive library is the use of multiple MediaAgents for processing reads/writes. Dynamic Drive capability is referred to as GridStor^® Technology. GridStor technology is an option that enables load balancing and failover of data protection jobs.

Virtual Tape Library (VTL)

A Virtual Tape Library (VTL) is a disk-based library that emulates the traditional tape devices and formats, and can be installed onto any disk space. Refer to the manufacturer's documentation to see if a disk-based storage subsystem supports VTL emulation mode. Follow the manufacturer's instructions to create the virtual tape library and make sure that the MediaAgent can detect the virtual arm changer and the drives created.

USB Devices - PnP (Plug and Play) Disk Libraries

For some environments with remote office locations connected to a main data center with limited bandwidth such as 'fractional T1' or 'satellite,' USB backup devices may provide the best protection solution. PnP (Plug and Play) Disk Libraries (USB devices) are configured and recognized by Commvault^® software as standalone tape devices. This allows data to be protected to USB devices using MediaAgents at remote locations, removed and sent to another location and connected to a different MediaAgent where the data can be accessed and restored. Since the USB device is detected as a tape device it is considered portable and any Windows MediaAgent within the CommCell^® environment can recognize the device and access/restore the data. This method can also be used for seeding stores when using Commvault deduplication for remote office protection.

A tape library is added directly from the CommCell^® browser by right-clicking libraries or using the expert storage configuration applet in the storage ribbon menu. The expert storage configuration applet provides advanced configuration options that are not available when using the CommCell browser add method.

Add a Tape Library

Before you configure a tape library in Commvault^® software, it first must be attached or zoned to be seen by the MediaAgent operating system. The device manager should detect one medium changer and one or many drives. It is recommended to install the vendor drivers specific to the library.

Once completed, if the library is dedicated to a single MediaAgent, it is configured directly in the CommCell^® browser. If it is shared, it must be configured using the Expert Storage Configuration wizard.

Tape Library Configuration Options

General Tape Library Configuration Options

Common configuration options are available for tape libraries.

Active and Failover Library Controllers

When a tape library is shared amongst multiple MediaAgents, only one of the MediaAgent acts as the active library controller. The active controller is responsible for sending SCSI commands to the device such as mounting/unmounting a tape, cleaning a drive, resetting a drive, exporting/importing media, etc.

Even if another MediaAgent requires writing data, the library operation is always conducted by the active controller. Failover candidates can be defined to replace the active controller, should the active controller become unavailable.

Virtual Mail Slots

When exporting media, the library uses I/E ports, also called Mail slots. If several tapes require to be exported and the number of I/E ports is limited, the tape operator must open the library multiple times, which triggers a library scan each time, wasting a lot of time. To avoid this situation, virtual mail slots are configured. Basically, the system uses defined regular slots to act as I/E ports. So instead of opening the library I/E ports, the entire magazine or library door can be opened to access the media.

When defining virtual mail slots, a starting port number must be defined, as well as the order for additional media. The order can go up or down. For instance, an administrator could define to start with port number one and to go up for additional media. Every day, the exported media will be ordered starting with port number one and will go up for as many slots are required.

When using virtual mail slots, ensure to leave at least one empty slot in the library, as it is required by the system when re-ordering tapes.

Appendable Media

By default, Commvault^® software tries to fill a tape completely before exporting it. This default behavior is overridden by either manually exporting the unfilled tapes or by scheduling an export media job using the 'Export Active Media' option. In such cases, the exported media is assigned a status of appendable. If the media becomes appendable but gets reinserted in the library within 14 days, it is used by the system for subsequent jobs. If it is reinserted after 14 days, the system does not use it anymore. The 14 days threshold can be modified to better fit your needs.

Media Container and Export Location Reset

When a tape is exported, its container and export location can be manually defined or defined by the Vault Tracker 'Export Media' job. When a tape is reinserted in the library, this information can be reset by checking the 'Reset container' and 'Reset export location' options in the library properties. These options can be enabled without any adverse effects and is useful when using Vault Tracker. It is recommended to enable these options.

Auto-Cleaning

Over time when using tape drives, dirt can accumulate on the drive read/write heads. When it happens it's important to clean the drives using a cleaning media. This process is usually automated but can be executed manually.

There are two different methodology when cleaning drives:

• Hardware Controlled Cleaning – The cleaning of the drives is handled by the library itself. In this scenario, auto-cleaning must be disabled in Commvault^® software and must be enabled on the library by using either the administration web portal or its control panel. The library configures dedicated cleaning slots where cleaning media are stored. The dedicated cleaning slots and cleaning media are not visible in Commvault software and cannot be used. Manual cleaning operations must be initiated from the library web page.
• Software Controlled Cleaning – The cleaning of drives is handled by Commvault software. In this scenario, auto-cleaning must be disabled on the library and must be enabled in Commvault software. The library does not reserve any dedicated cleaning slots and Commvault software is aware of the cleaning media. Cleaning must be initiated from Commvault^® software.

Both cleaning methods are equally effective since both use hardware sense code and/or cleaning thresholds. The preferred method can be determined based on the manufacturer's recommendations.

Even if both cleaning methods are as effective, it cannot be used concurrently. A choice must be made, and a single method used.

If the software receives a sense code and cleans the tape drive heads, but the drive still encounters errors, it is not a dirt issue and probably is a hardware malfunction that should be investigated. In this situation, to avoid having the system trying to clean the drive again, a minimal number of days since the last cleaning can be set before a new cleaning attempt is conducted. The default value is 3 days, which ensures that even on a long week-end, the administrator will notice that there is a cleaning issue before additional unnecessary cleanings are attempted. Otherwise, it could result in using all cleaning media in a single night.

When a drive status is set to dirty and the system cannot clean the drive, such as when there are no cleaning media available in the library, Commvault^® software stops using that drive completely for both backups and restores. This prevents damaging the media or corruption when writing data to the media a using dirty tape drive. If resources are limited and a restore requires a tape drive, the 'Continue using drive even if it needs cleaning, during the restore' option is used. It would allow using the drive, but as mentioned by the option, only during restores.

If you use cleaning thresholds, some adjustments to the threshold values might be preferable. By default, the threshold to retire a bad media is five read/write errors. But the threshold to clean a dirty drive is ten read/write errors, which means that up to two tapes could be retired before the drive gets cleaned. And these media are probably good media. To avoid this situation, you can slightly increase the tape threshold or decrease the drive threshold or both, to ensure that the drive is cleaned before the media is retired, (i.e., you could increase the tape threshold to seven and lower the drive threshold to six).

Overwrite Media Option

There are few media overwrite options that are set when configuring a tape library. These options apply to specific scenarios and should be carefully evaluated before planning on enabling it.

• When content verification fails – If enabled, when the MediaAgent encounters a media that it cannot read, such as a 'bad On Media Label (OML),' it automatically overwrites that tape. This option should be carefully planned as it could result in overwriting valid data.
• When it comes from a different CommCell environment – By default, when a tape was used in a different CommCell environment, Commvault^® software does not use the media and moves them into a media group called 'Foreign Media'. If desired, the media can automatically be used as scratch tapes by checking this option.
• Prevent use of tapes from a different backup vendor – This option is useful when the library is shared with another backup software. Since every vendor uses different writing format, Commvault software can identify a tape coming from a different vendor and prevent its use by checking that option.

Media Stuck in Drive

If a media is stuck in a drive for any reason, Commvault^® software offers few options to help resolving the situation.

• Enable Auto-Recovery – When this option is enabled, the MediaAgent tries to recover the Media every 20 minutes.
• Attempt to remove media from the drive when unload fails – When this option is enabled and the MediaAgent 'unload' command fails, it tries using a move command instead, which in some cases might successfully move the media out of the drive.

Unmount Idle Media Timeout

When a job completes, it does not automatically unmount the media that was used by the job. In fact, it keeps the idle media mounted for an additional 20 minutes by default. This is in case a new job requiring the same tape starts within 20 minutes, the media is already mounted and additional effort by the robotic arm is avoided. After 20 minutes of idle time, if the tape is not required by any job, it is then unmounted. During the 20 minutes of idle time, if another job requiring a different tape does not have any resource available, the idle tape is unmounted to accommodate the active job even if the time limit is not reached.

Tip: Automatic Auxiliary Copy Jobs to Tapes
Scenario: In recent versions of the software, auxiliary copy jobs are now scheduled to run automatically every 30 minutes. If you conduct frequent backups during the day, such as hourly transaction log backups, these jobs will be copied to tapes every 30 minutes. If the default value of 20 minutes is used to unmount idle media, tapes will constantly be mounted and unmounted for the entire day, which is definitely not recommended for the robotic arm.

Solution: Increase the 'Unmount Media from the drive after' value to 35 minutes. The first auxiliary copy job of the day then mounts the tape, which stays mounted all day long if no other jobs are requiring the drive.

Partitioned Library Recommended Options

When a tape library is partitioned and shared with another CommCell^® environment or another backup software, some options should be considered and could be beneficial as it ensures that the media are imported in the proper library partition.

• Do Periodic mail slot check for any change in status – This option periodically polls the library every 30 seconds for any change in the I/E ports status. The frequency of the polling is configured using the 'Library Status Check Interval' option.
• Prevent Auto Import of Media from mail slot – This option, when checked, prevents the MediaAgent from importing the media automatically when inserted in the mail slots. The import must be manually launched from the CommCell^® console.

Tape Library Associated Storage Policies

The Associations tab of a tape library displays all storage policies that have a copy sending data to the tape library. This is useful information when you plan on decommissioning a library or taking it offline for maintenance.

Drive Validation

A drive validation tests tape drive speed by writing and reading blocks of data to media. It is recommended to validate drives when the library is initially configured and to document the results. In the future, if you suspect having performance issues, a new validation job can be compared to the initial value.

Tape Library and Drive Status and Errors

The CommCell^® console easily provides library and drive status and errors information. For the library and drive status, simply click the library master drive pool. A status is displayed for each drive of the library. If a drive is displayed as offline, it can be a defective drive. If all drives are displayed as offline, it could indicate a communication or failure with the entire library.

If a library is offline, the library's Status tab, located within the Properties of the library, provides an explanation on the reason why. It also provides statistics and error counts. If counters start to increase, this could be an indication of connection errors or that a drive is about to fail.

To monitor progress, right-click the library and choose 'Mark Library Fixed' to reset counters and see if problem persists. A library can be disabled or taken offline for maintenance using the Status tab.

Tape Drive Replacement

Replacing a defective drive has an impact on backup software. Tape drives are mapped to their serial number in Commvault^® software. Some drive models now allow the serial number of the drive to be configured, which alleviates any impact on the backup system. But if the drive is not replaced with the same serial number, it must be addressed in Commvault software.

When the drive is replaced, right-click the old drive and choose 'Mark Drive Replaced.' After a few minutes, the system re-maps the drive to the new serial number and the drive becomes available. It is also possible to configure the system to attempt to remap replaced drives automatically. This is accomplished by enabling the automatic drive replacement in the library properties.