Microsoft IIS 6.0Administrator's Consultant

Guidelines for choosing hardware for Internet servers are much different from those for choosing other types of servers. A Web hosting provider might host multiple sites on the same computer and might also have service level agreements that determine the level of availability and performance required. On the other hand, a busy e-commerce site might have a dedicated Web server or even multiple load-balanced servers. Given that Internet servers are used in a wide variety of circumstances and might be either shared or dedicated, here are some guidelines for choosing server hardware:

• Memory The amount of memory that’s required depends on many factors, including the requirements of other services, the size of frequently accessed content files, and the random access memory (RAM) requirements of the Web applications. High-volume servers should have a minimum of 512 MB of RAM. More RAM will allow more files to be cached, reducing disk requests.

  Note

  Don't forget that as you add physical memory, virtual paging to disk grows as well. With this in mind, you might want to ensure that the Pagefile.sys file is on the appropriate disk drive.

  More Info

  For detailed information on memory management and performance tuning, see Chapter 13, “Performance Tuning and Monitoring.”

• CPU The CPU processes the instructions received by the computer. The clock speed of the CPU and the size of the data bus determine how quickly information moves among the CPU, RAM, and system buses. Static content, such as HTML and images, place very little burden on the processor, and standard Windows Server 2003 recommended configurations should suffice. Faster clock speeds and multiple processors increase the upper capacity of a Web server, particularly for sites that rely on dynamic content.

• SMP IIS supports symmetric multiprocessors (SMPs) and can use additional processors to improve performance. If the system is running only IIS and doesn’t rely on dynamic content or encryption, a single processor might suffice. You should always use multiple processors if IIS is running alongside other services, such as Microsoft SQL Server or Microsoft Exchange Server.

• Disk drives The amount of data storage capacity you need depends entirely on the size of content files and the number of sites supported. You need enough disk space to store all your data plus workspace, system files, and virtual memory. Input/output (I/O) throughput is just as important as drive capacity. However, disk I/O is rarely a bottleneck for Web sites on the public Internet—generally, bandwidth limits throughput. High-bandwidth sites should consider hardware-based redundant array of independent disks (RAID) solutions using copper or fiber channel–based small computer system interfaces (SCSIs).

• Data protection Unless you can tolerate hours of downtime, you should add protection against unexpected drive failures by using RAID. RAID 0 (disk striping without parity) offers optimal read/write performance, but if a drive fails, IIS won’t be able to continue operation until the drive is replaced. Because of this, RAID 0 isn’t the recommended choice. RAID 1 (disk mirroring) creates duplicate copies of data on separate drives, but recovery from drive failure might interrupt operations while you restore the failed drive from backups. RAID 5 (disk striping with parity) offers good protection against single-drive failure but has poor write performance. Keep in mind that if you’ve configured redundant load-balanced servers, you might not need RAID. With load balancing, the additional servers might offer the necessary fault tolerance.

• UPS Sudden power loss and power spikes can seriously damage hardware. To prevent this, get an uninterruptible power supply (UPS). A UPS system gives you time to shut down the system properly in the event of a power outage, and it’s also important in maintaining system integrity when the server uses write-back caching controllers that do not have on-board battery backups. Professional hosting providers often offer UPS systems that can maintain power indefinitely during extended power outages.

If you follow these hardware guidelines, you’ll be well on your way to success with IIS.