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Throughput and Connectivity - Frequently asked questions
Why is my throughput rate slower than advertised?
- Hardware - Check some common SCSI Adapter Card BIOS settings: a) Enable disconnect and enable Sync Negotiation should in most cases be set to NO b) Initiate Wide Negotiation should only be set to YES when the tape device is connected to a 68-pin wide SCSI connection.
- Available Memory - Insufficient memory, improper page file settings, and a lack of available free hard disk space will cause excessive paging and slow performance.
- Size and Number of Files - Fastest backups occur when the disk contains a few 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 will back up more efficiently compared to backing them up from multiple locations.
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How can I potentially improve my tape backup performance?
- Make sure your 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.
- Put the tape drive on a non-RAID controller by itself.
- Make sure that the settings are correct in the Controller's Post BIOS Setup Utility.
- Make sure that the proper driver/bios updates for the SCSI Controller have been applied.
- Confirm that the proper cabling/termination for the devices are being used. We recommend cables and terminators with gold pins for better conductivity. SCSI cables must meet the following specifications, SCSI-3 compliant, the Connector is a 68 pin micro D screw mount gold plated connector pins and the Cable is double shielded, foil and braid, SCSI 3 configuration.
- 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.
- Check the tape drive and tape media statistics to see if errors occur when backups run. If excessive errors show, the SCSI Controller Bios Settings. The Device Drivers, the BIOS/Firmware level or the type of tape media being used may be incorrect for the tape device.
- Run erase jobs on tapes and replace tape media as per the manufacturer's recommendations.
- Check the Windows NT or Windows 2000 system and application event logs for warnings/errors.
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During a tape backup or heavy I/O, I get ABENDS and drive deactivation. The system runs normally the rest of the time.
• Update to the latest SCSI adapter card driver.
• Change the Termination Power jumper or setting on all connected hard drives to "Disabled" or "from host adapter". The host adapter should provide the reference voltage for the SCSI device, not the device itself.
• Disable Write Cache on the hard drive. Consult your vendor to see if this feature is enabled, or if a utility or jumper can disable the feature.
• Replace the SCSI cable, device, or controller
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I have throughput problems using my backup software. Any tips?
• Software:
When we refer to software, we are not only referring to the backup software, but also referring to the o/s and third party software.
Make sure that latest service packs, and patches are applied.
This also applies to the o/s (WinNT or Windows 2000).
Virus scanning programs have been known to slow down backups. Many virus scanning software are designed to scan outgoing and incoming files. When the files are sent, the outgoing virus scanning will scan the data for viruses. This will impact the backup tremendously. A quick test is to disable the outgoing virus scanning, do a backup, and compare the throughput rate to when it's enabled. If the throughput is affected, disable the outgoing scanning of files.
• Hardware:There are many devices that can affect a backup. Many times it becomes difficult, to pinpoint which hardware device is the culprit. This section will take a look at the many devices involved, how they can affect the throughput, and the importance of all hardware being compatible.
• SCSI card:The SCSI card may be one of the most important items, when it comes to performing a backup or restore. Backup software generally does not use the manufacturer driver of the tape device (it is recommended that the driver is not loaded or disabled). The backup software communicates directly to the tape device, thru the SCSI card. It is very important that the SCSI card have the latest SCSI driver installed. The driver may become corrupt, and can cause throughput issues and backup errors. The driver should also be one that is certified by the manufacturer. Many SCSI drivers can be easily obtain and downloaded, at the manufacturers support web site.
• SCSI Cable:Use only shielded cables (foil and braid) with gold-plated connecter pins. Cables with tin or nickel connector pins do not provide a reliable contact and may oxidize over time. Cable must be SCSI 3 compliant.
• Tape Device:Some tape drives are capable of performing compression during backup. Compression routines may require overhead during a backup, and therefore decrease performance. At the expense of tape capacity, turning off hardware compression may increase performance. The software itself does not perform compression.
• Compatibility:Another major factor in receiving good throughput is making sure that all the hardware devices are compatible. Maximum throughput will be as fast as the slowest link on your network.
If you are backing up a client agent, and its NIC can only transmit 10mb per minute, and the server can transmit 100mb per second. Then the maximum throughput will be 10mb per minutes, regardless of other hardware capabilities.
• Network:One of the major factors a decrease in throughput can occur is because of your network. The backup software will use the resources of the network to perform a backup of remote machines. If there are issues with the Network, your backups will be affected. Anything from DNS problems, hardware issues, and configurations problems will result in a decrease in throughput, connectivity issues, and backup failures.
There are two items that we will focus on, that will help the throughput performance during backups. The two items are using half duplex versus full duplex, and using the Client Agent.
• Half duplex versus Full Duplex:Many network interface cards can be configured to use three settings. The three setting are auto detect, full duplex, and half duplex.
Full duplex is the process that allows two data streams to flow in opposite directions simultaneously. The receiving application can send control information back to the sending application while the sending application continues to send data.
Half duplex is the process where data may only move one direction at a time. It can communicate in both directions but only one way at a time.
Full duplex and half duplex can be seen as this. On a regular telephone, you can talk and listen at the same time: the telephone is a full-duplex device. With a portable radio walkie-talkie, on the other hand, as long as you hold down the "Talk" button, you can't hear anybody else who's trying to talk to you--that's why radio users say "Over" at the end of a transmission--so the other person knows you've finished and they can talk now. The walkie-talkie is half-duplex: it can communicate in both directions but only one way at a time.
It is recommended that a client uses half duplex. Half duplex transmits less data, which avoids less data collisions.
If you do decide to use half duplex, here is something to keep in mind. Do not use a mix node of half and full duplex settings. Make sure all hardware (NIC's, hubs, router, etc..) are configure the same; all full duplex or all half duplex. If the network is configured with half duplex devices interacting with full duplex devices, excessive collisions will occur which can cause connection problems
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I have a Dell server with an Adaptec 39160 and/or 29160 LVD SCSI Adapter Card. My throughput isn't as high as it should be, what could the problem be?
Make sure you have the drivers from Dell installed for your SCSI card and not the ones from Adaptec
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Why do my network backups to so long?
Potential problems may lie within the following:
- The amount of activity on the backup and client computers during the backup. Other applications (anti-virus software for example) running on either computer draw processing power away. Try a backup with your backup software as the only application running on the backup computer for optimal performance.
- File sharing:File sharing slows copying on both clients and the backup computer. Turning off file sharing when it's not needed can help optimize network performance.
- The performance of the backup and/or client computer:Problems with either machine affect the speed of your backup. Specifically, you should check for hard drive fragmentation, problems on the SCSI bus, and network problems.
- The speed of the backup computer.
- Location of the data you are backing up:If the data is located on a couple of large file servers, you should make them media server by physically connecting them to tape drives and maybe have one more to handle all the network-based clients. The restriction here will be the SCSI cable length restrictions from the media servers to the libraries.
- Speed of Network:If a significant amount of data resides on clients on a slow network, you should consider either installing a high-speed backup network or, if the is enough data, making one of these clients a media server. If possible, you should put the backup and recovery traffic on a dedicated network.
- Backup Window:You must always stay within the system constraints when configuring a media server. It does no good to put more tape devices on a server than it has the I/O bandwidth to handle. You do not want to create any unnecessary bottlenecks.
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