The ClusterLoad Nemasys load balancer, from ClusterScale

There may be plenty of server load balancing solutions on the market, but ClusterScale aims to offer a more cost-effective alternative to many of the main players. Its ClusterLoad family currently consists of three models with the Nemasys appliance (on review) aimed at mid-range businesses and enterprises. The Nemasys has at its foundation a Dell PowerEdge 1950 1U rack server and is equipped with a fine specification centred on a pair of 2.33GHz quad-core Xeon processors and 4GB of memory. Storage is handled by two 15K SAS hard disks configured in a RAID-1 mirror, and you also get a quartet of Gigabit network ports allowing link failover to be implemented. It also offers web server load balancing and Layer 4/7 content switching and can handle up to fourteen million concurrent L4 sessions.

The appliance uses the Xeon processors to provide SSL acceleration allowing it to handle 4,000 Transactions per Second (TPS). A key differentiator is that ClusterScale doesn't limit the number of supported physical and virtual servers. On review we have the more popular HA solution which comprises a pair of appliances linked via a serial cable for heartbeat operations. Installation was a simple process and made that much easier by ClusterScale's new console based wizard routine. In an HA environment, you start by locally configuring the slave first and then setting up the master using the same wizard. The reason for this is the slave needs to regenerate it's SSH encryption keys to allow the master to communicate with it. Another useful HA feature is the network Ping option which allows the master and slave to check availability of a designated device such as a router, via its IP address. The Nemasys supports a one-arm mode which uses one network port with physical and virtual servers on the same subnet and, unlike some of the competition it can perform Network Address Translation (NAT) in this mode.

More common is the two-arm mode where physical and virtual servers are placed in different subnets. Along with NAT routing, the Nemasys also supports DR (Direct Routing) and SNAT (Source NAT) between physical and virtual servers. DR provides a superior performance and allows virtual and physical servers to be on the same subnet, but it will need a loopback adapter installed on each server in the farm. We used the two-armed NAT mode for testing and created a server farm providing web, mail and FTP services to our test clients which were located on a different subnet.

During configuration you create a virtual server for each service and then associate your physical servers with it. Weightings are used for each server in the farm to set priorities for receiving requests and limits can be set on the minimum and maximum number of connections. Layer 4 persistence is determined by source and destination IP addresses, whilst Layer 7 inspection allows you to use functions such as cookies and URL switching to ensure clients are always sent to the same physical servers. During testing we had no problems with our test clients accessing the server farm for mail, FTP and web services and from the appliance's administrative interface we could see the round robin weighting in action when determining which server to send a client request to. To test the HA feature we powered down the master appliance during a test file copy and watched it continue whilst the slave reconfigured itself as the new master. The Nemasys looks good value when compared with some of the more established names, but ClusterScale hasn't sacrificed on features. It offers a solid range of server load balancing capabilities and is backed up by a very generous three year on-site warranty. NC

Product:

Nemasys Supplier: ClusterScale Ltd
Tel: 0844 669 8375
Web site: www.clusterscale.com
Price: Single appliance - £7,995, clustered pair - 12,995 (excluding VAT)