48 IBM eX5 Implementation GuideEach eXFlash can replace four 2.5-inch serial-attached SCSIs (SAS) or (SSDs). You caninstall the following number of eXFlash units: The x3850 X5 can have either of the following configurations:– Up to four SAS or Serial Advanced Technology Attachment (SATA) drives, plus theeight SSDs in one eXFlash unit– Sixteen SSDs in two eXFlash units The x3950 X5 database-optimized models have one eXFlash unit standard with space foreight SSDs, and a second eXFlash is optional.The x3690 X5 can have up to 24 SSDs in three eXFlash units.Spinning disks, although an excellent choice for cost per megabyte, are not always the bestchoice when considered for their cost per I/O operation per second (IOPS).In a production environment where the tier-one capacity requirement can be met by IBMeXFlash, the total cost per IOPS can be lower than any solution requiring attachment toexternal storage. Host bus adapters (HBAs), switches, controller shelves, disk shelves,cabling, and the actual disks all carry a cost. They might even require an upgrade to themachine room infrastructure, for example, a new rack or racks, additional power lines, orperhaps additional cooling infrastructure.Also, remember that the storage acquisition cost is only a part of the total cost of ownership(TCO). TCO takes the ongoing cost of management, power, and cooling for the additionalstorage infrastructure detailed previously. SSDs use only a fraction of the power, generateonly a fraction of the heat that spinning disks generate, and, because they fit in the chassis,are managed by the server administrator.IBM eXFlash is optimized for a heavy mix of read and write operations, such as transactionprocessing, media streaming, surveillance, file copy, logging, backup and recovery, andbusiness intelligence. In addition to its superior performance, eXFlash offers superior uptimewith three times the reliability of mechanical disk drives. SSDs have no moving parts to fail.They use Enterprise Wear-Leveling to extend their use even longer. All operating systemsthat are listed in ServerProven® for each machine are supported for use with eXFlash.The eXFlash SSD backplane uses two long SAS cables, which are included with thebackplane option. If two eXFlash backplanes are installed, four cables are required. You canconnect the eXFlash backplane to the dedicated RAID slot if desired.In a system that has two eXFlash backplanes installed, two controllers are required in PCIeslots 1 - 4 to control the drives; however, up to four controllers can be used. In environmentswhere RAID protection is required, use two RAID controllers per backplane to ensure thatpeak IOPS can be reached. Although use of a single RAID controller results in a functioningsolution, peak IOPS can be reduced by a factor of approximately 50%. Remember that eachRAID controller controls only its own disks. With four B5015 controllers, each controllercontrols four disks. The effect of RAID-5 is that four disks (one per array) are used for parity.You can use both RAID and non-RAID controllers. The IBM 6Gb SSD Host Bus Adapter(HBA) is optimized for read-intensive environments, and you can achieve maximumperformance with only a single 6Gb SSD HBA. RAID controllers are a better choice forenvironments with a mix of read and write activity.The eXFlash units can connect to the same types of ServeRAID disk controllers as the SASand SATA disks. For higher performance, connect them to the IBM 6Gb SAS HBA or theServeRAID B5015 SSD Controller.
