Sizing Guide Exchange Server 2003 - Fujitsu

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White Paper Sizing Guide Exchange Server 2003 Version: 4.2, July 2006 Computing performance It is obvious that the more powerful the processor, the more processors in a system, the faster the data are processed. However, with Exchange the CPU performance is not the only decisive factor. The Microsoft Exchange server provides an acceptable performance even with a relatively small CPU configuration. In fact it is important that a fast disk subsystem and an adequate memory configuration are available and, of course, that the network connection is not a bottleneck. It becomes especially evident with small server systems that the processor performance is not the restricting factor, but the configuration options of the disk subsystem. The diagram opposite can be used as a guideline for the number of processors. There are no strict limits defining the number of processors. All systems are available with 4 processors of different performance. Thus a 2-way system with highly clocked dual processors and a large cache can by all means be within the performance range of a poorly equipped 4- 1 2 way system. Which system is used with regard to possible expandability ultimately depends on the forecast of customer‟s 500 1000 2000 3000 4000 User growth rates. In addition, it could prove advantageous to also use a 2-way or 4-way system for a smaller number of users, as this type of system frequently offers better configuration options for the disk subsystem. As far as pure computing performance is concerned, 4-way systems are generally adequate for Exchange Server 2003, because with large Exchange servers it is not computing performance but Exchange-internal memory administration that sets the limits. However, it may still make sense to use an 8-way system if very CPU-intensive Exchange extensions are used in addition to the pure Exchange server or if with regard to greater availability the use of Windows Server 2003, Datacenter Edition is taken into consideration. With more than approximately 5000 active users on a server the scaling of Exchange Server is not satisfactory (see Main memory). Therefore, for large numbers of users a scale-out scenario, in which several servers in a logical array can serve an arbitrarily large number of mail users, should be considered instead of a scale-up scenario. Main memory As far as the main memory is concerned, there is a quite simple rule: the more the better. Firstly, the main memory of the server must at least be large enough for the system not to be compelled to swap program parts from the physical memory into the virtual memory onto the hard disk. Otherwise this would hopelessly slow down the system. As far as the program code is concerned, 512 MB would generally suffice. The system would then run freely and no program code would have to be swapped out to the hard disk. If, however, more memory is available, it is then used by Exchange as a cache for the data from the Exchange database, the so called store. This leads to what could be classed as a substantial load relief for the disk subsystem and thus a gain in performance. After all, accesses to the memory are about 1000 times faster than accesses made to the hard disks. But unfortunately there are also limits here. On the one hand 4 GB RAM is a magical limit. It is not possible to address any more with a 32-bit address. Windows 2000 and 2003 have mechanisms for overcoming this limit, the so-called Physical Address Extension (PAE). Depending on the version, Windows supports up to 128 GB RAM. From a hardware viewpoint, it would also be unproblematically possible to provide this memory in the PRIMERGY RX600 S3 or RX800 S2, but Microsoft Exchange Server 2003 does not support these PAE address types and is as regards addressing limited to 4 GB RAM. Further information is available at Physical Address Extension - PAE Memory and Windows [L18]. © Fujitsu Technology Solutions, 2009 Page 16 (69) # CPU # CPU RAM [MB] /3GB Support Windows 2000 4 4 - Windows 2000 Advanced 8 8 � Windows 2000 DataCenter 32 32 � Windows 2003 Standard 4 4 � Windows 2003 Enterprise 8 32 � Windows 2003 DataCenter 32 64 � Windows 2003 Standard SP1 and R2 4 4 � Windows 2003 Enterprise SP1 and R2 8 64 � Windows 2003 DataCenter SP1 and R2 64 128 �
White Paper Sizing Guide Exchange Server 2003 Version: 4.2, July 2006 A further reduction in the effective memory results from the system architecture of Windows Server 2003. Thus this address space is divided by default into 2 GB for the operating system and 2 GB for applications, to which Exchange is also classed. By means of an appropriate configuration parameter it is possible to shift this split to 1:3 GB in favor of the applications. It is advisable to use this so-called /3GB option as early as a physical memory configuration of 1 GB RAM. (For better understanding: this /3GB option refers to the administration of virtual memory addresses, not to the physical memory.) The option /USERVA, with which the distribution of the address space at 3:1 can be controlled in a more detailed way, was introduced with Windows Server 2003 as a supplement to the /3GB option. The necessity of the /3GB switch for Exchange becomes clearer under the effect that Exchange obviously requires about twice the number of virtual addresses in proportion to the physically used memory, which Microsoft describes only indirectly. This effect can be explained from a program point of view and even regarded as a good or at least modern programming style because of the underlying methodology. Based on the fact that with 32-bit systems the limits of available virtual addresses and physically available memory are coming closer and on the fact that even the physical memory exceeds the addressable memory, this memory administration architecture represents an (unnecessary) limitation. In other words, it could be assumed that an IA64-bit system, such as the PRIMERGY RXI600, is the optimal system for Exchange. Reality, however, is that a 64-bit architecture would be optimal for the internal memory administration of Exchange Server 2003, but not for the other components of Exchange Server 2003. Thus there is at present no 64-bit version of Exchange Server 2003 so that despite the almost infinite virtual memory space of 8 TB (terabyte), which is provided by 64-bit Windows to applications, Exchange would from today's perspective not run faster in the present version on an IA64-bit system, but more slowly. But let's return to the current hardware options. At a rough estimate: 3 GB of virtual address space for Exchange, of which at most half can be used physically, results in 1.5 GB. In fact, Microsoft has limited the ESE cache size for the store to about 900 MB. According to a Microsoft description, this may be increased to 1.2 GB. Please note: This memory requirement is only for the store cache. It goes without saying that Exchange Server 2003 uses additional memory for other data. With 2 GB RAM an Exchange server is already quite well equipped. What lies above a memory configuration of 3 GB is only used conditionally by Exchange. However, a configuration with further memory of up to 4 GB can be very practical if other components, such as a virus scanner or fax services, are to be added in addition to Exchange. In addition to these considerations as to the maximum (sensibly) effective memory, there are also guidelines based on empirical values, which calculate memory configuration on a user basis. Microsoft recommends you to calculate 512 kB RAM per active user. If you assume a base of 512 MB for the operating system and the core components, the outcome is the linear lower curve opposite RAM = 512 MB + 0.5 MB * [number of users] If this is reflected against the limitations discussed above, it is also possible to read an upper limit of users that an individual Exchange server can serve: approximately 5000 users. This is not a fixed limit. It is by no means so that the Exchange server crashes with a higher number of users, it is simply no longer able to function efficiently with a high load. On account of a lack of memory the disk subsystem is put under a greater load. Due to higher throughput times the load placed on the CPU is ultimately also increased. More jobs have to be managed in the queues, this in turn causes a higher administration outlay and greater memory requirement, which is ultimately at the expense of the cache memory. Thus a process escalates in such a way that in the end all users can no longer be adequately served. In addition, practical experience has shown that »small« systems in particular benefit from a somewhat larger memory configuration (see upper curve). © Fujitsu Technology Solutions, 2009 Page 17 (69)
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