Many variables can affect throughput performance of backups and restores. These can include:
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 improper cabling/termination can slow performance. Confirm that the controller is rated for the tape backup hardware. That is, don't expect high speeds of a 120MB/Second tape drive connected to a 10 MB/Second SCSI controller. Check that the SCSI Bios Settings are set properly as follows:
Initiate Wide Negotiation is set to Yes when the tape device is connected to a 68 pin wide SCSI Cable Connector.
Tape drives are not connected to a SCSI Raid Controller.
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 to 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.Make sure that when any program or process starts the amout of memory it consumes at the start it should release the same at the end of the same process or program (it is also called memory leak).
Definition: Memory leak
The amount of memory consumed by any process should also be released when the process stops or terminates ,if its not doing so then its called Memory leak.
File Types
The average file compresses 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 disk. 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. Compression can be highly variable depending on the input data. 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 when attempting 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 can 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. The default block size set by NetVault Backup does not need to be increased beyond the default.
Network
The backup speed for a remote disk is limited by the speed of the physical connection. The rate at which a remote server's hard disks are able to be backed up depends on:
The make/model of network cards.
The mode/frame type configuration for the adapter.
The connectivity equipment (hubs, switches, routers, and so on).
System Settings.
Local disk drives on the media server can usually be backed up at a faster than backing up remote servers across a network.
A common reason for slow network backups can be networking configuration.
Features such as "full-duplex" and "auto-detect" may not be fully supported in every environment. Manually set the speed to 100 Mb and the duplex to half/full for the server side. Find out which Ethernet port the server is connected to on the switch, and set the SWITCH PORT setting to 100 MB and half/full duplex. Do this for the backup server switch port, and any switch ports for machines being backed up.
Note: When a hub is in place instead of a switch, full duplex may not be supported, see the Original Equipment Manufacturer for details on device features.
Note: Both the switch and the network card must have matching settings, for instance, if the switch port is set to 100 half, the NIC for the server should also be set to 100 half.
If a full duplex backup is slower than the half duplex backup, full duplex may not be supported for the combination of NIC, driver and switch. Contact the NIC and Switch manufacturer for updated drivers, firmware, or other support documentation.
Another common cause could be the NIC driver. The NIC driver can be easily overwritten by an operating system service pack. If a service pack has been applied and the driver has been overwritten, reinstall the Original Equipment Manufacturer (OEM) driver.
Checking ALL of these variables will most likely lead to the answer behind the poor performance. Software itself, has very little impact on backup performance, but every so often there could be something in the software that can cause issues. Normally though, if this was the case, you would see the issues across all NV Clients, not just a select few.
