PAC STORAGE PS 3012 Hardware Manual
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33Maximum Concurrent Host LUN Connection (“Nexus” in SCSI)The "Max Number of Concurrent Host-LUN Connection" menu option is used to set themaximum number of concurrent host-LUN connections.Maximum concurrent host LUN connection (nexus in SCSI) is the arrangement of thecontroller internal resources for use with a number of the current host nexus.For example, you can have four hosts (A, B, C, and D) and four host IDs/LUNs (IDs 0,1, 2 and 3) in a configuration where: Host A accesses ID 0 (one nexus). Host B accesses ID 1 (one nexus). Host C accesses ID 2 (one nexus). Host D accesses ID 3 (one nexus).These connections are all queued in the cache and are called four nexus.If there is I/O in the cache with four different nexus, and another host I/O comes with a nexusdifferent than the four in the cache (for example, host A accesses ID 3), the controllerreturns busy. This occurs with the concurrent active nexus; if the cache is cleared, it acceptsfour different nexus again. Many I/O operations can be accessed via the same nexus.Maximum Queued I/O CountThe "Maximum Queued I/O Count" menu option enables you to configure the maximumnumber of I/O operations per host channel that can be accepted from servers. Thepredefined range is from 1 to 1024 I/O operations per host channel, or you can choose the"Auto" (automatically configured) setting. The default value is256 I/O operations.The appropriate "Maximum Queued I/O Count" setting depends on how many I/Ooperations the attached servers are performing. This can vary according to the amount ofhost memory present as well as the number of drives and their size. But usually, optimumperformance results from using the "Auto" or "256" settings.For more information, please refer to the Firmware Manual that came with your system.Fibre-Host ConnectionsWARNINGAll Fibre cables are sensitive and must be handled with care. To avoid interference,the cable routing path must be carefully planned and the cables must not be bent.The Fibre Channel standard allows optical connections. Optical cables can be used overlonger distances and have been shown to be more reliable. Due to the demands of hightransfer rates, optical cables are preferred for 16/ 8/ 4Gbps fiber connectivity. Optical cablesare not susceptible to EMI.The Fibre host ports connect to Fibre Channel host adapters (HBA) that feature SFPinterface that supports full-duplex transfer and come with a PCI-E interface. Please contactyour vendor for the latest certified items. |
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