Bob, You can read ioql as "IO queue length" (outside of GPFS) and "qsdl" as QOS queue length at the QOS throttle within GPFS, computed from average delay introduced by the QOS subsystem.
These "queue lengths" are virtual or fictional -- They are computed by observing average service times and applying Little's Law. That is there is no single actual queue but each IO request spends some time in the OS + network + disk controller + .... For IO bound workloads one can verify that ioql+qsdl is the average number of application threads waiting for IO. Our documentation puts it this way (See 4.2 Admin Guide, mmlsqos command) iops= The performance of the class in I/O operations per second. ioql= The average number of I/O requests in the class that are pending for reasons other than being queued by QoS. This number includes, for example, I/O requests that are waiting for network or storage device servicing. qsdl= The average number of I/O requests in the class that are queued by QoS. When the QoS system receives an I/O request from the file system, QoS first finds the class to which the I/O request belongs. It then finds whether the class has any I/O operations available for consumption. If not, then QoS queues the request until more I/O operations become available for the class. The Qsdl value is the average number of I/O requests that are held in this queue. et= The interval in seconds during which the measurement was made. You can calculate the average service time for an I/O operation as (Ioql + Qsdl)/Iops. For a system that is running IO-intensive applications, you can interpret the value (Ioql + Qsdl) as the number of threads in the I/O-intensive applications. This interpretation assumes that each thread spends most of its time in waiting for an I/O operation to complete. From: "Oesterlin, Robert" <[email protected]> To: gpfsug main discussion list <[email protected]> Date: 03/08/2016 10:53 AM Subject: [gpfsug-discuss] Interpreting "mmlsqos" output Sent by: [email protected] So – I enabled QoS on my file systems using the defaults in 4.2 Running a restripe with a class of “maintenance” gives me this for mmlsqos output: [root@gpfs-vmd01a ~]# mmlsqos VMdata01 --sum-nodes yes QOS config:: enabled QOS values:: pool=system,other=inf,maintenance=inf QOS status:: throttling active, monitoring active === for pool system 10:36:30 other iops=9754 ioql=12.17 qsdl=0.00022791 et=5 10:36:30 maint iops=55 ioql=0.067331 qsdl=2.7e-05 et=5 10:36:35 other iops=7999.8 ioql=12.613 qsdl=0.00013951 et=5 10:36:35 maint iops=52 ioql=0.10034 qsdl=2.48e-05 et=5 10:36:40 other iops=8890.8 ioql=12.117 qsdl=0.00016095 et=5 10:36:40 maint iops=71.2 ioql=0.13904 qsdl=3.56e-05 et=5 10:36:45 other iops=8303.8 ioql=11.17 qsdl=0.00011438 et=5 10:36:45 maint iops=52.8 ioql=0.08261 qsdl=3.06e-05 et=5 It looks like the “maintenance” class is getting perhaps 5% of the overall IOP rate? What do “ioql” and “qsdl” indicate? Bob Oesterlin Sr Storage Engineer, Nuance HPC Grid 507-269-0413 _______________________________________________ gpfsug-discuss mailing list gpfsug-discuss at spectrumscale.org http://gpfsug.org/mailman/listinfo/gpfsug-discuss
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