Symantec Backup Exec

Hardware

The speed of the disk controller and hardware errors caused by the disk drive, the tape drive, the disk controller, the SCSI bus, or the improper cabling/termination can slow performance.

Confirm that the controller is rated for the tape backup hardware and that the SCSI Bios Settings are set properly. Newer models of SCSI Controllers are set to communicate with SCSI Hard Drives by default. Most tape drives can only handle a maximum sync transfer rate (bus speed) of between 3 to 22 MB/sec when utilizing hardware compression. Speed in excess of this will not only affect the ability for data to write to the tape in a continuous stream, but can also potentially damage the tape hardware.

System

The capacity and speed of the media server performing the backup, or the remote system being backed up significantly impacts performance. System activity during backup also impacts performance.

Fragmented disks take a longer time to back up. Heavily fragmented hard disks not only affect the rate at which data is written to tape, but also affect the overall system performance. Fragmented files take longer to back up because each segment of data is located at a different location on the disk, which causes the disk to take longer to access the data. Make sure you defragment disks on a regular basis.

Memory

The amount of available memory will impact backup speed. Insufficient memory, improper page file settings, and a lack of available free hard disk space will cause excessive paging and slow performance.

See System requirements.

File Types

The average file can potentially compress at a 2:1 ratio when hardware compression is used. Higher and lower compression occur depending on the type of files being backed up. Average compression can double the backup speed, while no compression runs the tape device at its rated speed.

Image and picture files are fully compressed on disks. Therefore, no hardware compression takes place during the backup causing the tape drive to operate at its native (non-compression) rate of speed. Hardware compression is performed by the tape device and not the backup software.

Compression

Successful compression can increase the tape drive’s data transfer rate up to twice the native rate. Some tape drives use the Lempel-Ziv (LZ1) compression algorithm for its superior versatility and efficiency. Compression can be highly variable depending on your input data. Compression algorithms look for repeatable data patterns that can be compacted.

Image files from a graphical program like Microsoft Paint, may compress at 4.5:1 or more, while binary files may compress at just 1.5:1. Data that has already been compressed or random data (such as encrypted data or MPEG files) may actually expand by about five percent if you attempt to compress it further. This can reduce drive throughput.

Files

The total number of files on a disk and the relative size of each file impacts backup performance. Fastest backups occur when the disk contains fewer large size files. Slowest backups occur when the disk contains thousands of small files. A large number of files located in the same directory path back up more efficiently than backing them up from multiple directory locations.

Block Size

Larger block sizes improve the compression ratio, which helps the drive to achieve better throughput and more tape capacity. Make sure that the block and buffer size are set properly. The throughput will increase in proportion to the compression achieved, until the drive’s maximum throughput is reached.

Some devices (for example, DLT devices) provide better performance when larger block sizes are used. The preferred block size can range from 512 bytes to 64 kilobytes or larger. If you use a device that supports larger block sizes, you can change the device’s block size in the Device Configuration tab. However, if the option to change the block size is unavailable, you must configure the device to use a larger size.

See the device manufacturer’s documentation for help to configure the device.

Network

The backup speed for a remote disk is limited by the speed of the physical connection.

Local disk drives on the media server can usually be backed up at a higher rate of speed than backing up remote servers across a network.

Hardware

The speed of the disk controller and hardware errors caused by the disk drive, the tape drive, the disk controller, the SCSI bus, or the improper cabling/termination can slow performance.

Confirm that the controller is rated for the tape backup hardware and that the SCSI Bios Settings are set properly. Newer models of SCSI Controllers are set to communicate with SCSI Hard Drives by default. Most tape drives can only handle a maximum sync transfer rate (bus speed) of between 3 to 22 MB/sec when utilizing hardware compression. Speed in excess of this will not only affect the ability for data to write to the tape in a continuous stream, but can also potentially damage the tape hardware.