Reasons why the data throughput rate can be slower than the theoretical maximum when backing up to or restoring from tape media or disk (B2D) & how to troubleshoot or improve backup performance

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Reasons why the data throughput rate can be slower than the theoretical maximum when backing up to or restoring from tape media or disk (B2D) & how to troubleshoot or improve backup performance.



Backup and restore performance varies between similar systems, and the backup performance of any system is directly related to one or more of the following performance factors:




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.


Can get very slow performance while backing up to a Backup to Disk folder created on  an external USB drive that supports USB 2.0 and if the media server supports just USB 1.0


Confirm that the controller is rated for the tape backup hardware and that the SCSI Bios settings are set properly. That is, make sure that the controller has sufficient bandwidth to fully utilize the tape drive to its rated speed.  The tape drive is not going to be able to run at a 120 MB/Second if the controller is only capable of transmitting at 10 MB/Second


Initiate Wide Negotiation should only be set to Yes when the tape device is connected to a 68-pin wide SCSI cable connector.


A tape drive should not typically be connected to a SCSI Raid Controller.


Destination drives that are setup with RAID 5 can show degraded performance. RAID 10 has been shown to significantly improve overall performance. In some cases, RAID 10 offers faster data reads and writes than RAID 5 because it does not need to manage parity.


RAID 10 = Combining features of RAID 0 + RAID 1. It provides optimization for fault tolerance.


RAID 0 helps to increase performance by striping volume data across multiple disk drives.


RAID 1 provides disk mirroring which duplicates your data.

2. System

Disk/File Fragmentation - 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, so instead of simply reading block after block of data, the heads on the disk must travel to a number of places to access the data. Performance can usually be improved by performing regular disk defragmentation.


System activity during a backup will also slow performance to the tape drive.  Along with less system activity, make sure there are plenty of free disk space on the system volume (C:\ drive).

3Available  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.

4File Types

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


Image and picture files are fully compressed on disks. Therefore, when backing up these types of files, no hardware compression takes place, which means that the tape drive is operating at its native (non-compression) rate of speed. Hardware compression is performed by the tape device and not the backup software.


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. 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 when attempting to compress it further. This can reduce drive throughput.

6Size and Number of Files

The total number of files on a disk and the relative size of each file can either speed up backup or slow it down. The fastest backups occur when the disk contains a few large size files. The slowest backups occur when the disk contains thousands of small files. A large number of files located in the same directory path will back up more efficiently compared to backing them up from multiple locations.

7Block Size

The bigger the block sizes the better the compression ratio. With better compression ratio, the drive is able to achieve not only better throughput, but also increased capacity on the tape. Confirm 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. Symantec does not recommend increasing the Block Size above the default settings.


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), and Windows. Local disk drives on the Backup Exec Server can usually be backed up at a higher rate of speed than backing up remote servers across a network.

9Network settings:

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.

 What is the Optimal Throughput?


Host processor speed, host adapter performance, bus configuration, host software, and disk drive characteristics and performance are all considerations. On many systems it is possible to get a sense of the maximum data transfer rate possible, regardless of the tape drive, with a copy to a null file from disk. When this rate is lower than the throughput specifications, it is likely that improvements will have to be made in the host before the drive can reach its maximum transfer rate. 

To test the performance of the local system and network drives, perform a test backup that best suits an optimized backup rate. An example might be a backup of a few large files, which will compress at a rate of at least 2:1 ratio on a disk relatively free of fragmentation, and not having any other activities performed at the same time. To calculate the optimized compression backup rate, multiply the native tape drive speed by two and then multiply the result by 60 for an MB per minute rate (then multiply by 60 for a MB per hour rate).  Then divide by 1024 to get GB/hour (1024MB=1GB).

NOTE: The following calculation is an example of the theoretical maximum rate as provided by the hardware vendor specifications for the devices. This rate may not actually be attained due to bottlenecks due to system hardware, opening/closing of files, other simultaneous activity involving the CPU/Memory, slow network speeds, data types, and either I/O or tape errors. 

A DLT 7000 tape drive will be calculated as follows: 5 MB/Sec x 2 x 60 = 600 MB per minute x 60 / 1024 = 35 GB per hour
An LTO-4 tape drive will be calculated as follow: 120 MB/Sec x 2 x 60 = 14400 MB per minute x 60 / 1024 = 843 GB per hour


            How to potentially improve tape backup performance:


1. Make sure the tape drive is properly defined for the host system. It is common for a SCSI host to disable the adaptive cache on the drive if it doesn't recognize the product identification string returned by an inquiry command. This cache enables features like drive streaming to operate at peak performance. See the product manual for more details on this.

2. Put the tape drive on a non-Raid controller by itself

3. Make sure that the settings are correct in the controller's Post Bios Setup Utility

4. Make sure that the proper driver/Bios update for the SCSI Controller have been applied

5. Confirm that the proper cabling/termination for the devices are being used

6. Update the firmware on the tape drive to the latest level. In some rare cases, the firmware may actually need to be downgraded to improve performance.

7. Check the Preferred Configuration Settings for the tape drive and verify that they are set properly

8. Check the tape drive and tape media statistics to see if errors( soft- hard read/write) occur when backups run. If excessive errors show, the SCSI Controller Bios Settings, the Device Drivers, the Bios/Firmware Level, Bad media or the type of tape media being used may be incorrect for the tape device.

9. Run erase jobs on tapes and replace tape media as per the manufacturer's recommendations

10. Check the Windows System and Application Event Logs for warnings/errors. Event IDs 7, 9, 11, and 15 in the System Event Log usually indicate that there is a hardware problem.


1. If Media Server is inside a network firewall open the ports in the firewall for Backup Exec to communicate with the remote server.

You may need to open application specific ports mentioned in the following Article:

2. If Anti-Virus is installed on a Media Server and/or remote server open the ports and add an exception for  Backup Exec installation directory.

113rd party software:

Check for other software and related services that may be accessing the same data sets or media.







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