52 IBM eX5 Implementation Guidebe assigned to SSD storage. When you must use memory swap files, assign the swap filespace to conventional SAS or SATA hard drives.2.10.2 SSD drives and battery backup cache on RAID controllersWhen using conventional SAS or SATA hard drives on a ServeRAID controller, it is commonpractice to enable writeback cache for the logical drive to prevent data corruption if a loss ofpower occurs.With SATA SSD drives, writes to the drives are immediately stored in the memory of the SSDdrive. The potential for loss of data is dramatically reduced. Writing to writeback cache firstand then to the SSD drives actually increases the latency time for writing the data to the SSDdevice.Today’s SSD optimized controllers have neither read nor writeback cache. If you are in a solidSSD environment, the best practice is to not install a RAID battery and to not enable cache.When your storage uses a mixed media environment, the best practice is to use aServeRAID-5xxx controller with the IBM ServeRAID 5000 Performance Accelerator Key.We describe this topic in detail in the following sections: IBM System x3690 X5: 4.9.1, “2.5-inch SAS drive support” on page 145 IBM System x3850 X5: “ServeRAID M5000 Series Performance Accelerator Key” onpage 952.10.3 Increased resources for virtualizationThe huge jump in processing capacity and memory allows for the consolidation of services,while still maintaining fault tolerance using scalable clustered host solutions. As your serversapproach peak demand, additional hosts can be automatically powered on and activated tospread the computing demand to additional virtual servers as demand increases. As the peakdemand subsides, the same environment can automatically consolidate virtual servers to asmaller group of active hosts, saving power while still maintaining true fault tolerance.By using larger servers with built-in redundancy for power, fans, storage access, and networkaccess, it is now possible to combine the functional requirements of a dozen or more serversinto a dual-hosted virtual server environment that can withstand the possible failure of acomplete host. As demand increases, the number of hosts can be increased to maintain thesame virtual servers, with no noticeable changes or programming costs to allow the samevirtual server to function in the new array of hosts.With this capability, the server becomes an intelligent switch in the network. Instead of tryingto balance network traffic through various network adapters on various servers, you can nowcreate a virtual network switch inside a cluster of host servers to which the virtual serverslogically attach. All of the physical network ports of the server, provided that they are thesame type of link, can be aggregated into a single IEEE 802.3ad load balance link tomaximize link utilization between the server and the external network switch. Two scaledx3850 X5s running in a clustered virtualized environment can replace an entire 42U rack ofconventional 1U servers, and their associated top rack network and SAN switch.2.10.4 Virtualized Memcached distributed memory cachingMany web content providers and light provisioning providers use servers designed for speed,and not fault tolerance, to store the results from database or API calls so that clients can beredirected from the main database server to a MemCached device for all future pages within
