NetVault 12.2 - Administration Guide

Device Serial Number

Displays the drive serial number.

End of media warning

This option specifies the amount of media reserved at the end of the tape at which the “end of media” warnings are issued. This value is specified in MB. The default value is 0MB.

Time between polling empty drive

This option specifies the interval at which NetVault Backup polls a standalone drive to detect a tape in the device. This value is specified in number of minutes. The default value is one (1).

To turn off polling, set this option to zero (0).

Media block size (KiB)

This option specifies the block size used for read and write operations. The default value is 64KiB.

You can change the media block size in increments of 1KiB, but many devices may only accept a value in the multiples of 4KiB or 32KiB.

Increasing the block size can reduce the number of times a backup needs to read data and write it to media. However, large media block sizes do not always imply an overall faster backup. The maximum block size is limited by several factors, such as the OS, SCSI adapter, drive make, drive model, and drive type.

On Linux and UNIX systems, you can increase the media block size for optimum performance.

On Windows, you might be required to change the registry setting MaximumSGList to use block sizes larger than 64KB. Before changing this setting, check that the SCSI bus is only used by the tape devices. If other devices also use the SCSI bus, this registry change might prevent them from working. If you want to apply these changes only to a specific channel on the HBA, consult the hardware vendor.

To change the registry setting on Windows, follow these steps:

Time to wait for plugin to connect

This option specifies the timeout period for the plug-in to connect to NetVault Backup. The job is aborted if connection cannot be established within the specified interval. This value is specified in number of seconds. The default value is zero (0). With the default setting, the job is not timed out.

Supports Short Reads

The default setting is ON. To change it, press the option number.

Cleaning Tapes Supported

This option indicates whether the library supports cleaning tapes or not. The default value is usually correct, unless certain library models have a different setting.

Compression

This option allows you to use a tape drive’s built-in compression feature. Not all tape drives support hardware-based data compression. The compression ratio varies depending on the type of data and the compression algorithm that the drive uses. Consult the hardware documentation to determine the compression ratios for the drive.

Perform software data compression

The default setting is OFF. To perform software compression, change the setting to ON. The data is compressed when it is transferred to the device during backup.

Compression decision switch

The value set for this option determines the minimum level of compression that must be achieved when data is compressed during a backup. For example, if you set the value to 80 percent, one of the following occurs:

If you specify 80 percent, a file size of a 100MB must be <= 80MB after compression however, the file size can be >80MB (like 81MB, 82MB, etc.), as the compression is done at block level.

When the specified compression level is not achieved for any block, in that case NetVault Backup backs up that block in its uncompressed form. Where, some blocks may be compressed and some blocks may remain in uncompressed form. Hence, in some case, the file size after compression can be greater than 80 percent.

The extent that data can be compressed depends on the data contents. Also the encrypted data cannot be compressed. With some files, compression may actually result in a file that is larger than the original uncompressed file.

Number of data blocks per compression unit

Type the number of data blocks per compression unit. The default block size is 8KiB.

Open disk media for Synchronous IO on Unix

The default setting is OFF. If your RAID system can respond instantaneously to synchronous IO writes, change the setting to ON. The ON setting allows multiple streams to generate output at similar rates resulting in similar jobs ending at the same time (but at the expense of overall throughput).

Under most circumstances, it is best to leave this option at the default OFF state to achieve best overall performance.

Amount of memory to assign for transfer buffers

The transfer buffer or the shared memory is allocated in blocks of 32KiB. The default value is 8193KiB.

Increasing the transfer buffer size can improve backup performance. To calculate the buffer size, use the following formula:

(<Total number of buffers> x 32KiB) + 1 byte

On Linux and UNIX systems, you require sufficient RAM and large Shared Memory segment. Before increasing the transfer buffer size, check the following settings on these platforms:

The total allowed shared memory is determined by the formula SHMMAX * SHMSEG. These values are often limited by the ulimit setting, and the command ulimit -a can be used to view these system settings.

On Windows, you require at least 2GB RAM and large virtual memory. You might also have to change the MaximumSGlist setting on the SCSI card.

For examples, see the Optimal transfer buffer size.

Number of media blocks to write at a time

We recommend that you do not change the default setting for this option.

If you change the value, record it because it is necessary to re-apply the setting if the drive is reinstalled. Restores require the same values that are set at the time of backup and fail if the settings do not match.

Number of media blocks to read at a time

We recommend that you do not change the default setting for this option.

If you change the value, record it because it is necessary to re-apply the setting if the drive is reinstalled. Restores require the same values that are set at the time of backup and fail if the settings do not match.

Lock transfer buffer in memory

Use this option to lock the allocated transfer buffer position in memory, and thus increase the potential performance and prevent other processes from using it when NetVault Backup is running.

The default setting is ON. Do not change the default setting unless otherwise advised by Quest Technical Support.

Gather statistics on device performance

The default setting is OFF. To log drive performance statistics, change the setting to ON. This information facilitates troubleshooting. However, it also increases the size of the NetVault Database.

Gather statistics on data channel performance

The default setting is OFF. To log Data Channel statistics, change the setting to ON. This information facilitates troubleshooting. However, it also increases the size of the NetVault Database.

Record drive performance

The default setting is ON. To record drive performance details with each job that uses the drive, use the default setting.

Length of time between sampling drive transfer rates

Specify the interval at which NetVault Backup records the drive transfer rates. The value is specified in number of seconds. The default value is 60 seconds.