6.4 Best practice 4: Select the right disaster recovery technology


6.4 Best practice #4: Select the right disaster recovery technology

There is a plethora of backup technologies, techniques, and strategies available in the Windows environment. From a technology point of view, choosing the right technology for your deployment involves both hardware and software. In addition, the storage technology you select for your Exchange deployment will have a significant impact on what options are available to you for disaster-recovery. From a best practices point of view, you will need to select the technology that best meets your unique requirements. Table 6.2 provides some basic criteria for selecting backup software. There are many different vendors who offer excellent backup software products. Industry leaders such as Computer Associates, Veritas, Legato, and CommVault Systems are among the most often selected for Exchange deployments. Each vendor offers a different mix of features, device support, and cost. All have different trade-offs. For example, in my experience, Legato Networker provides the best heterogeneous operating system support but, in my experience, is weakest in hardware device support. Computer Associates’ ArcServe product, on the other hand, has better device support, but supports fewer operating system choices. All vendors have different strengths and weaknesses. You will need to select the vendor that best meets the needs of your Exchange deployment and disaster-recovery requirements. As the Exchange system administrator, your organization may have already selected a standard, and you may not have the luxury of choosing.

Table 6.2: Recommended Backup Software Selection Criteria

Selection Criteria

Description

Client/server architecture

Client-server architecture applied to backup software results in a solution with two or more components. Some products use a two-tier or three-tier architecture for their solution; most important is the ability to back up on remote tape drives or, inversely, to back up locally remote server information.

Scheduling capabilities

Scheduling capability enables “lights-out” operations for the backup facility. For instance, a backup should be run at a given point in time with certain conditions. Such operations will require the ability to report backup status to a central management station.

Exchange API support

As explained earlier, the on-line backup capability resides in the implementation of a backup agent that uses the Microsoft Exchange backup API to access to the database information. Online backups do not require Microsoft Exchange to be shut down for saving the information.

Tape management capabilities

Most software products provide some support for automatic tape labeling, including bar code generation, cataloging, and librarian functions for proper archiving and identification. This function is important when dealing with a large quantity of information to back up, for full or incremental backups.

Vendor support

This refers to how well the vendor supports its product offering including technical support, updates, and patches, as well as platform support.

Tuning/tweaking/scripting capabilities

This refers to the degree to which the software provides advanced tuning capabilities via the registry or other mechanisms that allow the software to be configured optimally for all scenarios.

Device support

As new tape devices and other backup subsystems and media such as automated libraries and other devices are developed, how quickly a vendor provides support for these new devices is critical.

Operating System Support

Since most organizations have more than one operating system deployed, support for multiple operating systems may be required so that the organization can utilize a single product for all disaster-recovery needs, including Exchange Server.

Disaster-recovery management and tools

Many vendors provide complete disaster-recovery planning and other tools that provide total disaster-recovery management and that allow complete recovery via a disaster-recovery disk or other means.

Cluster support

Many backup vendors do not specifically test or develop with cluster scenarios in mind. If you are considering clustering your Exchange servers, this is an important criterion.

SAN and NAS support

SANs and NAS storage systems add some additional degree of complexity to the environment. It is important for backup vendors to have developed and tested with high-end storage systems in mind.

Advanced features

Support for Redundant Array of Independent Tapes (RAIT), SAN-direct backup and restore, and other advanced techniques and technologies should be an important consideration when selecting a backup software vendor. Also, with the advent of Windows VSS, support for this new technology is another criterion to look for in your vendor.

In addition to selecting the backup software technology that best meets your organization-specific needs, you will need to put careful thought into the hardware technology choice to which you will marry that software. There are many options for devices to use as your media of choice for storing critical backup sets required to recover your Exchange servers. Quarter Inch Cartridge (QIC), Digital Audio Tape (DAT), Advanced Intelligent Tape (AIT), Digital Linear Tape (DLT), and Linear Tape-Open (LTO) are among the most popular options. However, each type of media has advantages and disadvantages. When selecting your media option (and therefore your hardware device option), many points need to be weighed. In addition, each option will have a different cost point that must be justified. In some cases, the cost of the device and media may be relatively low, but come at some cost in terms of reliability. In other cases, the most reliable option may also be the most expensive. Your choice of backup devices and media for your Exchange deployment will have to weigh all the technological, reliability, and cost factors against your organization’s disaster-recovery requirements. Table 6.3 includes some important criteria for selecting media and devices.

Table 6.3: Recommended Backup Device/Media Selection Criteria

Selection Criteria

Description

Vendor support

In the case of both backup devices and media, multiple vendors offer products. As in the case of backup software, the degree to which the vendor supports its product is important. Vendors should provide technical support and updates (such as firmware updates) for device hardware.

Configuration flexibility

Many vendors offer backup devices that can be configured in a variety of ways such as stand-alone, RAIT, or multi-streaming. Flexibility of configuration provides more options for successful disaster-recovery.

Capacity

Different device/media options have different capacities. For example, DLT media comes various capacities and SDLT extends this even further. In addition, different levels of hardware and/or software compression are also available.

Speed/rate

Device performance is critical and this factor can vary from technology to technology, as well as from vendor to vendor.

Interface/connection

Devices may be offered with several interface options such as SCI, SCSI, or Fibre Channel attachment. Depending on growth and future flexibility needs, you may prefer one interface option to another.

Automation

Some devices are offered in the form of automation products such as carousels and libraries. If automation is key to your backup and recovery plans, selecting products that are offered in these form factors is a must.

Error detection/correction

Technologies such as LTO, DLT, AIT, DAT, QIC, and others all offer varying degrees of error-detection and correction capability. Understand what each technology offers and select the one best suited to your needs.

Cleaning duty cycle

Some technologies have very high cleaning duty cycles and require frequent cleaning and/or maintenance. QIC and DAT technologies are an example of this. DLT, SDLT, and LTO, on the other hand, require less frequent cleaning and maintenance.

Head/drive/tape life

The operational life of the tape drive and head will vary depending on the technology you choose.

Compatibility

QIC, DAT, AIT, and DLT have all evolved over several years and generations of technology. If you are archiving media for long periods, ensure that future devices will have compatibility with previous technology evolutions.

Cost

The cost of your technology choice will have long-term impacts. The cost of both devices and media will need to be considered.

I have always preferred DLT drives and array technology over other devices and media. I also believe it to be the most widely used device/media option for Exchange deployments today. However, I am seeing LTO in more and more Exchange deployments. While more costly, both LTO and DLT offer superior capacity, reliability, performance, and drive and tape life than QIC or DAT. While QIC and DAT may be less expensive and feasible for smaller deployments and organizations, they cannot match the strengths of DLT technology. DLT technology also offers more flexibility of configuration. DLT drives can be used stand-alone as individual drives or can be configured in RAIT arrays for increased performance, capacity, and reliability. A relative newcomer to tape technology is AIT. AIT provides many of the performance and reliability features that DLT provides but at a somewhat lower cost. The tape technology game is much like any other technology in that the various products and technology are engaged in an eternal game of leapfrog where technology benefits are concerned. Whatever your choice for backup media, make sure you understand the pros and cons of each technology and which is the bet fit for your Exchange deployment and organization’s needs.

In the race to get high backup throughput, the alternative to fast and expensive tape drives is to use multiple DLTs. In fact, most vendors can support up to 28 DLT tape drives or more, with resulting backup rates over 800 GB per hour and even higher (unfortunately, not for Exchange). The backup and restore operations for Microsoft Exchange are single stream for the most part. The exception is when multiple storage groups are backed up simultaneously (which may have a net result of slower overall performance due to Exchange Server resource contention). It is not possible to back up several parts of the single-file databases at the same time. Using multiple tape drives requires selecting backup software that efficiently streams data to multiple tape drives in parallel. The common terminology is RAIT, and levels 0 and 5 (distributed parity) are commonly in use. Legato Networker, CA ARCserve, and Veritas Backup Exec/Net Backup are examples of backup software that handle multiple tape drives. I recommend only using RAIT5 or any RAIT with redundant parity; the data stream being strictly sequential, the generation of the parity will not degrade the performance to a large extent. Similar to multiple tape drive “striping” (using RAIT) are the benefits of multiple tape drive streaming. In this scenario, independent backup or restore operations to different datasets are performed simultaneously as multiple “streams.” This can occur from separate storage groups on an individual Exchange server, or streams can come from multiple Exchange servers via the storage area network or the local area network. Tape drive striping and streaming are both excellent methods of increasing backup and restore speeds by allowing the concept of concurrency (either block concurrency or stream concurrency) in your Exchange backup and restore operations.

To compress or not to compress is an interesting question: compression allows storing more information faster, but the rate at which an Exchange database, which is already somewhat compressed for text body parts, is compressed is not known. When in doubt, I suggest using compression whenever available, but you will need to make a choice between either software-based compression (done by the backup software) or hardware-based compression. The software-based compression has its advantages, such as transferring less data over the network in the case of client/server backup operations; on the other hand, the tape-level compression is done at the tape hardware level and is presumably faster than the software compression. Again, the CPU capacity of the client and the server will impact actual performance.

The products you select form the foundation of your disaster-recovery capability. If you select products that limit your ability to provide adequate recovery of your Exchange servers, your disaster-recovery service levels will not be achieved. A well-planned disaster-recovery procedure will be worthless if the technology upon which you base the procedure does not deliver what it promises. Hopefully, you have the option of selecting the right backup software, device, and media in advance of putting your disasterrecovery plan in place. Make every effort to thoroughly evaluate the vendors and technologies available using the criteria discussed above, as well as criteria dictated by your own organizational or deployment needs. The balance you strike between criteria such as performance, reliability, and cost will enable you to build a solid disaster-recovery plan for your Exchange deployment. This will help you meet your mission-critical SLAs.




Mission-Critical Microsoft Exchange 2003. Designing and Building Reliable Exchange Servers
Mission-Critical Microsoft Exchange 2003: Designing and Building Reliable Exchange Servers (HP Technologies)
ISBN: 155558294X
EAN: 2147483647
Year: 2003
Pages: 91
Authors: Jerry Cochran

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