The number of users a XenApp server can support depends on several factors, including:
- The server’s hardware specifications
- The applications deployed (CPU and memory requirements)
- The amount of user input being processed by the applications
- The maximum desired resource usage on the server (for example, 90% CPU usage or 80% memory usage)
General recommendations for selecting and configuring farm hardware include:
- RAID - In multiprocessor configurations, Citrix recommends a RAID (Redundant Array of Independent Disks) setup. XenApp supports hardware and software RAID.
- Reducing hard disk failure - Hard disks are the most common form of hardware failure. You can reduce the likelihood of hardware failure with a RAID 1 (mirroring) and RAID 5 (striped set with distributed parity) configuration. If RAID is not an option, a fast Serial Attached SCSI (SAS) or a Small Computer System Interface (SCSI) Ultra-320 drive is recommended.
- Disk speed - Faster hard disks are inherently more responsive and might eliminate or curtail disk bottlenecks.
- Number of controllers - For quad or eight-way servers, Citrix recommends installing at least two controllers: one for the operating system and another to store applications and temporary files. Isolate the operating system as much as possible, with no applications installed on its controller. This principle also applies in small farms. If possible (assuming a multicore or multiprocessor system), install the operating system on a separate hard drive from XenApp and the applications. This prevents input/output bottlenecks when the operating system needs to access the CPU. Distribute hard drive access load as evenly as possible across the controllers.
Dual-processor (dual-core) deployments combine overall efficiency and a lower total cost of ownership. However, once a system has a dual-core processor, implementing additional processors does not necessarily provide proportionate performance increases. Server scalability does not increase linearly with the number of processors: scalability gains level off between eight to sixteen CPU cores.
- Hard disk partitions - Partition and hard-disk size depend on the number of users connecting to the XenApp server and the applications on the server. Because each user’s Remote Desktop Services profile is loaded on the server, consider that large numbers of user profiles can use gigabytes of disk space on the server. You must have enough disk space for these profiles on the server.