Under certain conditions a local disk can performance better than an array LUN (overhead for network, remote cache vs on-board cache, disk caching locally, etc.). Using 15K FC disks, each disk can handle a sustain workload of about 180 IOPS or 12MB/s for larger IO's (larger than 32KB). The more sequential the better the performance - Reads vs. Writes, random vs sequential, small block vs large block.  When you create a Raid 5 raid group using 5 disks, a 4+1, a single LUN in this raid group can handle 5 * 180 IOPS = 900 IOPS or 12MB/s * 5 = 60MB/s.  For more detailed information - look in the Documents section on the forum and find the Best Practices guide for the version of flare on your array. There is a section in there about determining the number of disks required to handle a workload.  glen
I am having a problem with PowerPath 5.3 SP1 and a Win 2008 server.    After installing powerpath I am only get 29 IOPS per used path with occasional spikes to up to 130.  Only two path  are used out of the four which is to be expected.   If I set all but one path to be in standby the IOPS on the only active channel goes up and maintains at least 680 IOPS.   This does not seem to be related to a specific channel or controller because ever path can consistently sustain 680 IOPS if is the only channel used.    The server has to NIC's (BC5716)   in it, each attaching to a different iscsi network.     The networks are 10.70.160.0/24 on one NIC and 10.70.140.0/24 on the other.   The CX4 has 4 iscsi ports total, 2 on each controller.   SPA2  and SPB2 are connected to 10.70.140.0/24 and SPA3 and SPB3 are connected to 10.70.160.0/24.  I have the made all the changes in the registry that are recommended by EMC and have the latest firmware and drivers for the NIC's   Any suggestions?
iSCSI Multipath problem with CX4 and Windows 2008