AIX for System Administrators 2020-06-03 14:00:00

fcstatThe fcstat command reports statistics directly from the FC adapter firmware and the FC driver. Protocols such as TCP/IP are designed to tolerate packet loss and out-of-order packets with minimal disruption, but the FC protocol is in-tolerant of missing, damaged or out-of-order frames and is incapable of re-transmitting a single missing frame.This moves error recovery into the SCSI layer and can result in waiting for commands to timeout. In some cases an error frame is not detected by either the target or the initiator, so it just waits for completion until 30 or 60 seconds to timeout. These are often the result of a physical layer problems such as a damaged fibre channel cable, faulty or degraded laser in SFP’s (in a storage controller, switch or host) or perhaps a failing a ASIC in a switch or a slow draining device causing frames to be discarded. Regardless of the cause, identifying and resolving fibre channel transport related problems are necessary before any I/O performance tuning is attempted.It is also important to ensure the SCSI layer does not overwhelm the Target Ports or LUNs with excessive I/O requests. Increasing num_cmd_elems may result in driving more I/O to a storage device resulting in even worse I/O service times. (errpt, and iostat can help uncover some of these problems.) However acceptable I/O service time can differ.  For example, some shops demand less than 2 ms service times where others may tolerate 11 ms. The disk technology affects expected I/O service time, as does the availability of write and/or read cache.If queuing in the disk driver is occurring, (iostat shows non-zero value in qfull) this should be resolved first like increasing queue_depth, or adding additional storage resources (if io service times are too high).  After ensuring there are no fibre channel physical layer problems, average I/O response times are in good range (not exceeding 15 ms) and there is no queuing (qfull) in the disk driver, then we can tune the adapter.———————————–In normal way fcstat resets statistics when server is rebooted or the fcs device is reconfigured. fcstat -Z fcsX can be useful for daily monitoring because it resets statistics.fcstat fcsX        shows fc adapter statisticsfcstat -D fcsX     shows additional fcs related detailsfcstat -e fcsX     shows all stats, which includes the device-specific statistics (driver statistics, link statistics, and FC4 types)fcststat -Z fcsx   resets statistics———————————–root@aix1:/ # fcstat fcs0FIBRE CHANNEL STATISTICS REPORT: fcs0Device Type: 8Gb PCI Express Dual Port FC Adapter (df1000f114108a03)(adapter/pciex/df1000f114108a0)Serial Number: 1C041083F7Option ROM Version: 02781174ZA: U2D1.11X4                                      <–firmware versionWorld Wide Node Name: 0x20000000C9A8C4A6           <–adapter WWNWorld Wide Port Name: 0x10000000C9A8C4A6           <–adapter WWPNFC-4 TYPES: Supported: 0x00000120000000000000000000000000000000000000 Active:    0x00000100000000000000000000000000000000000000Class of Service: 3Port Speed (supported): 8 GBIT                     <–8Gb adapterPort Speed (running):   8 GBIT                     <–running at 8GbPort FC ID: 0x6df640       …

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