StorageTek's white paper explains how to configure SAN system components to obtain the best storage routing performance.
Configuring Storage Routers for Maximum EfficiencyDECEMBER 2004A PPLICATION NOTEUntitled Document1Configuring Storage Routers for Maximum EfficiencyAPPLICATION NOTEExecutive summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 The challenge of SAN configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Applying the solution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22.1 Tape drive evaluation using the LTO Gen 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22.2 Router evaluation using the StorageNet 3300 storage routers. . . . . . . . . . . . . . . . . . . . . . 32.3 Router evaluation using the StorageNet 3400 multi-protocol routers . . . . . . . . . . . . . . . . . 33 Benefits of optimizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Untitled Document2Configuring Storage Routers for Maximum EfficiencyAPPLICATION NOTEExecutive summaryMany IT installation customers have trouble determining the best con guration for connecting SCSI tape drives to SANs via Fibre Channel routers. Their needs can vary, from getting the best capacity from their infrastructure, to getting the best performance. Some customers throw hardware at a performance problem, when instead, by understanding how a device works and making adjustments accordingly, they can improve performance and save money.There are different advantages with the various possible con gurations for connecting SCSI tape drives to SANs. Understanding these differences, along with the capabilities and bene ts of the hardware involved, can help you determine what your best con guration will be. By using a con guration designed speci cally for your needs, you can save considerable time and money. One good methodology for con guring an effective routed storage solution entails identifying the bottlenecks in your system architecture and optimizing the other components to deal with this limitation. This document describes the use of Linear Tape Open (LTO) Ultrium tape drives con gured with StorageTek s StorageNet 3300 storage routers and StorageNet 3400 multi-protocol routers to a SAN to illustrate this methodology. However, this same methodology can also be applied to any device.1 The challenge of SAN con gurationA good understanding of the application environment is important to con guring a SAN. Poorly understanding the environment can lead to either over-con guring the SAN, resulting in too much cost, or under-con guring it, resulting in an inadequate storage con guration. Developing an appreciation of your application environment provides the foundation for creating a SAN appropriate to that environment for an appropriate cost.When connecting tape drives to the SAN, a signi cant consideration is what the tape drive s function will be. The majority of time it is for backup solutions, but equally important is the host capability and data volume being backed up. If the hosts getting backed up cannot deliver the data as fast as the router can handle it, you do not have to worry about the aggregate bandwidth of the router. The router will have excess capacity relative to the load being delivered by the application server. But if these hosts and data are of a high-performance nature, evaluate where any possible bottlenecks can be and how to avoid them.The key to evaluating performance bottlenecks is to model and understand where the potential bottlenecks are, and what impact they will have in your speci c deployment. The bottlenecks are driven by the application mix that is being served. Understanding that mix in the context of the storage technology characteristics sets the foundation for more accurately planning your storage con guration and growth needs more accurately. 2 Applying the solution2.1 Tape drive evaluation using the LTO Gen 2First, let s look at the IBM LTO Ultrium Generation 2 tape drives. Their performance characteristics are speci ed as:.. Native sustained data transfer rate of 35 megabytes per second.. Compressed data transfer rate of up to 70 megabytes per secondThe up to variable is important to understand, even though every tape drive manufacturer uses this potentially confusing terminology. This variable is dependent upon many circumstances, one of which is the compressibility of the data. This can also skew all of the calculations of bandwidth utilization, but the fact is that very few applications are going to push the native rate to the maximum, much less the compressed rate to the maximum. Seventy megabytes per second is the maximum compressed data rate that the drive can sustain regardless of the compressibility of the data. The gating factor becomes the speed of the compression chip. Although the example calculation of compressed data rates is based upon 2:1 compression, in fact, it could be greater than that.It is possible that an application will burst to these speeds, but it is unlikely two drives will peak at the same time. Deciding on what speci cation native or compressed you should use depends on the goal of your con guration. If it s to gain maximum speed, use the compressed rate when planning what router to use and the native rate for the tape drive. This will give you maximum bandwidth on the router, and no shortage of tape drives. If cost is a factor and you want to be conservative with equipment expenses, you may want to use native speeds when planning the router and compressed performance on the tape drive. This will result in a smaller router and fewer tape drives. These are the extreme boundaries that delineate a range of options between performance and cost. A good rule-of-thumb is to base all tape drive speeds on maximum native performance specs. This should leave some room for bursting. To ne tune the rule-of-thumb, it s always a good idea to ask the backup administrators what transfer rate they are currently experiencing, and then adjust your rates accordingly.Untitled Document3Configuring Storage Routers for Maximum EfficiencyAPPLICATION NOTE2.2 Router evaluation using the StorageNet 3300 storage routersJust as with the tape drives, it is important to dissect the SN3300 router speci cations:.. One Fibre Channel port (2 Gb at 80% ef ciency transfers 160 MB/sec).. Two SCSI buses, one port per bus; each bus is an Ultra 160 type (160 MB/sec at 90% ef ciency transfers 144 MB/sec ) The FC port is rated at 160 MB/sec. This means:.. 160 MB/sec divided by 35 MB/sec (native rate) = 4.57 drives.. 160 MB/sec divided by 70 MB/sec (2:1 compression) = 2.2 drivesOne SCSI bus is rated at 144 MB/sec. This means:.. 144 MB/sec divided by 35 MB/sec (native rate) = 4.1 drives per bus or 2 buses times 4.1 drives per bus = 8.2 drives.. 144 MB/sec divided by 70 MB/sec (2:1 compression) = 2.05 drives bus or 2 buses times 2.05 drives per bus = 4.05 drivesLooking at the two components SCSI bus and FC port we can determine the number of drives needed using either speci cation: native speed versus compressed speed. The component with the lowest number of supported drives at native speed is the FC port itself at 4.57 drives: 160 MB/sec ----------------------------- = 4.57 drives per FC port 35 MB/secThe component with the lowest number of supported drives at compressed (2:1) speed is also the FC port at 2.2 drives: 160 MB/sec ----------------------------- = 2.2 drives per FC port 70 MB/secDepending on your requirements, a safe compromise could be to use two or three drives maximum. Even if two drives were running maximum native speed (35 megabytes per second), the third drive could still run at maximum compressed speed (70 megabytes per second) with some comfort. Knowing the application or data type is key to calculating how you should build your con guration and what type of throughput you could expect. If the data is not compressible, more resources in terms of tape drives and router capacity are required to meet the application s backup requirements.2.3 Router evaluation using the StorageNet 3400 multi-protocol routers The SN3400 router is very exible in its con guration; it can handle up to four I/O modules. The two types of module available are:Fibre Channel module Two 2-Gbit FC connectors SCSI module Four SCSI Ultra 3 buses/connectorsThe default con guration is one of each module.Let s break down the speci cations for the SN3400:.. One Fibre Channel module with 2 ports can handle (at 80% ef ciency) 160 MB/sec times 2 = 320 MB/sec.. One SCSI module with 4 SCSI buses (Ultra 3) can handle 160 MB/secThe internal router s aggregate bandwidth is 300 MB/sec, which means:.. 300 MB/sec divided by 35 MB/sec (native) = 8.5 drives per card.. 300 MB/sec divided by 70 MB/sec (2:1 compression) = 4.2 drives per cardThe SCSI bus has 4 SCSI buses per card, which means: .. One SCSI bus rated at 160 MB/sec (at 90% ef ciency) = 144 MB/sec per bus.. 144 MB/sec times 4 buses = 576 MB/sec per card.. 576 MB/sec divided by 35 MB/sec (native) = 16.45 drives per card.. 576 MB/sec divided by 70 MB/sec (2:1 compression) = 8.22 drives per cardThe dual FC port can handle 320 MB/sec, which means:.. 320 MB/sec divided by 35 MB/sec (native) = 9.14 drives per card.. 320 MB/sec divided by 70 MB/sec (2:1 compression) = 4.57 drives per cardLooking at the three components SCSI bus, FC port and internal processing we can determine the number of drives needed for both native speed and compressed speed. The component with the lowest number of supported drives at native speed is the router itself at 8.5 drives.The component with the lowest number of supported drives at compressed (2:1) speed is the router at 4.2 drives.Untitled Document4Configuring Storage Routers for Maximum EfficiencyAPPLICATION NOTEThese calculations make it clear how the native and compressed throughput can have a big impact on your con guration. Knowing the application or data type is key to calculating how you should build your con guration and what type of throughput you could expect. If the data is not compressible, more resources in terms of tape drives and router capacity are required to meet the application s backup requirements.Depending on your requirements, a safe compromise could be to use a maximum of ve or six drives. Even if four drives are running maximum native speed (35 megabytes per second), drives ve and six could still run at maximum compressed speed (70 megabytes per second) with some comfort.3 Bene ts of optimizingYou can apply this methodology, which breaks down a device or network to determine bottlenecks, to most devices and networks. Whether it s a host platform (CPU, bus, I/O architecture) or an entire network (LAN type, WAN connection, router type), identifying the slowest component will help you ascertain the cost-bene t ratio of improving that component. Once you know where your potential bottlenecks are, you can properly assess their potential impact in your environment. This will help you determine the scalability of your con guration and when you will reach your limit and need to recon gure or add additional resources. By having your con guration designed to your speci c needs, you avoid over-purchasing new equipment and optimize the equipment you already have.A baseline understanding of your application environment provides a foundation for anticipating and managing storage con guration changes. For instance, if new applications are planned, you can model and forecast the storage network changes required to support those applications. The ability to accurately forecast these changes allows your enterprise to accurately budget for them and minimize their cost.Cheater s Corner As a starting basis without performing the calculations, here are two shortcut rules-of-thumb you can use. The aggressive con guration is appropriate when maximum performance is of primary importance. Use the conservative con guration when you want to avoid unnecessary equipment expenses.Aggressive con guration (performance bias)Conservative con guration (cost bias)SN3300 routerFour LTO Gen 2 drivesTwo LTO Gen 2 drivesSN3400 routerEight LTO Gen 2 drivesFour LTO Gen 2 drivesUntitled Document 2004 Storage Technology Corporation, Louisville, CO. All rights reserved. Printed in USA. StorageTek and the StorageTek logo are registered trademarks of Storage Technology Corporation. Other names mentioned may be trademarks of Storage Technology Corporation or other vendors/manufacturers. StorageTek equipment is manufactured from new parts, or new and used parts. In some cases, StorageTek equipment may not be new and may have been previously installed. Regardless, StorageTek s standard warranty terms apply, unless the equipment is speci cally identi ed by StorageTek as used or refurbished. Replacement parts provided under warranty or any service offering may be either new or equivalent-to-new, at StorageTek s option. Speci cations/features may change without notice. ABOUT STORAGETEK Storage Technology Corporation (NYSE: STK) is a 2 billion global company that enables businesses, through its information lifecycle management strategy, to align the cost of storage with the value of information. The company s innovative storage solutions manage the complexity and growth of information, lower costs, improve ef ciency and protect investments. For more information, visit www.storagetek.com, or call 1.800.275.4785 or 01.303.673.2800.WORLD HEADQUARTERSStorage Technology CorporationOne StorageTek DriveLouisville, Colorado 80028 USA1.800.877.9220 or 01.303.673.5151NT 0001 A 12/04