Cherwell Server Farms Q&A

Question: Could I take one physical box, divide it into two virtual machines, and install CSM services on them as two different participants of the server farm?

Answer: Yes, but we do not recommend it. One of the purposes of the farm is to eliminate having a single point of failure. If the hardware below the two virtual machines fails, the entire farm goes down, making the purpose of the farm useless. Having the two virtual machines reside on different hardware is a better option.

Question: Can I mix and match server types on a single box?

Answer: Yes. You would have to make some performance and high availability considerations to determine which servers can reside together.

Question: How do I know if I have to separate my servers onto multiple machines with a dedicated machine, or if I can share a machine across multiple Cherwell servers?

Answer: Depending on the size of the machine and the performance load, you might find that a shared machine is not enough.

Question: How many servers in a Cherwell server farm should be deployed to match the performance of a single standalone server, and why?

Answer: Three load-balanced servers should be deployed to match the performance of a single standalone server in the event that one of them fails. This is because of the overhead associated with the Cherwell server farm topology. CSM clients in the load-balanced environment can appear slightly slower because of session state serialization and Redis traffic.

Question: What are the bandwidth and latency requirements for the Cherwell server farm?

Answer: Network interfaces should provide high bandwidth and very low latency. For example, 10GbE interconnects to high capacity hardware-switched aggregators that provide near 100 percent wireline throughput bi-directionally with no backplane over-subscription and nanosecond latency performance.

Process Servers

Question: Can CSM services (Automation Processes, E-mail and Event Monitoring, Mail Delivery, and Scheduling) be load-balanced?

Answer: CSM services use a centralized queue to enable the distribution of workload. For more information, see Scaling the Cherwell Service Host.

Question: Can these non-load-balanced services be set up for high availability?

Answer: Yes, using Windows Server Fail-over Clustering with the Generic Service or VM Clustering.

SQL Server

Question: What type of cluster model does Cherwell recommend for SQL Server?

Answer: Always-On Availability Groups.

Question: What is the formula for determining the total amount of disk storage needed?

Answer: A starting best practice is to allocate 600 MB of storage per licensed user per year. If routinely saving large attachments to records, this formula should be doubled.

Question: When using SANs to store SQL data, are there any special considerations?

Answer: Yes. Differentiate networks between SAN traffic and other traffic, such as communications between applications servers, SQL, and Redis. Storage for SQL data should be on different spindles than other data.

Question: Does SQL Server have to be set up on a dedicated, physical machine?

Answer: We highly recommend that SQL Server run on dedicated hardware or on virtual machines with dedicated CPU cores, memory, and dedicated physical storage. It was Microsoft's position to say "never run SQL Server on a virtual machine". SQL is optimized in how it accesses memory and deals with the file system. Microsoft has backed away from this firm stance, although it still recommends running SQL on physical, dedicated machines. If SQL is run on a virtual machine, memory and CPUs CANNOT be oversubscribed. It is still recommended that SQL hit physical disks (or NAS) and not a virtual file system. Dedicated is best. If you give SQL 'X' amount of memory and another process on that machine suddenly takes the memory away, it drastically affects SQL's performance.

Question: Does SQL Server need to be set up on the same LAN as the application and process servers?

Answer: Not required, but highly recommended. High throughput and low latency is the goal for best performance.

Question: Should SQL Server files be distributed across separate disks?

Answer: Yes. For example, separate data, logs, temp, and database files.

Load Balancer

Question: Can software-based load balancers be used for Cherwell's server farm solution?

Answer: Yes, as long as they are set up properly. IIS ARR is an example of a software load balancer solution, although we do not recommend it. To use it, ensure that all of its response-caching features are disabled.

Question: What are the key performance indicators of a load balancer?

Answer: Maximum throughput, SSL throughput, SSL transaction per second (TPS) based on key size - typically 2048 - HTTP requests per second.

Question: For health monitoring, which application may be monitored to indicate server online state?

Answer: /CherwellService application pool is a good candidate for this; others can be used.