6 Replies Latest reply: Feb 3, 2014 2:02 AM by 1010552 RSS

    VDbench response time

    1010552

      Hi,

       

      I am using VDbench on AIX.

       

      For this case I am using a workload with a particular characteristics (Read %, Hit % etc..) with I/O rate - 500 IOPS, the whole I/O rate could be achieved on the subsystem. A portion of the corresponding flatfile.html (5 secs interval) is as below:

       

               tod             Run   Interval    reqrate       rate          MB/sec        bytes/io      read%       resp        resp_max   resp_std   xfersize    threads      rdpct           rhpct      whpct

      01:09:59.569    User1          10   500.0000   460.6000   115.1500     262144     0.0000     8.6923   189.9990    14.8417     262144          4              0.0000    20.0000    20.0000

      01:10:04.342    User1          11   500.0000   522.2000   130.5500     262144     0.0000     5.0896    90.4090     7.4483     262144          4                0.0000    20.0000    20.0000

      01:10:09.339    User1          13  500.0000   501.0000   125.2500     262144     0.0000     4.5735    85.2520     7.1220     262144          4                 0.0000    20.0000    20.0000

       

      VDbench shows the response time average over 5 seconds interval under "resp" column and the maximum during the last 5 seconds interval under "resp_max" column. My doubt is where from VDbench gets the response time data for each I/O. I guess the response time capture has to be for each I/O to know the maximum.

       

      Please let me know if you have any questions.

       

      Thanks in advance.

      1010552

        • 1. Re: VDbench response time
          Henk Vandenbergh-Oracle

          Since Vdbench starts each i/o itself, it knows when the i/o starts and when the i/o completes. The difference of these two equals the response time.

           

          Henk.

          • 2. Re: VDbench response time
            1010552

            Hi Henk,

             

            Thanks for your reply. Is there any way to understand what were the stages of any particular I/O, i.e.:

             

            1. The time stamp when VDbench starts / stops counting on an I/O.

            2. The time stamp, I/O request actually leaves the host to enter storage (In the case above I/O is being sent to storage LDEV (No filesystem)).

             

            Thanks.

            • 3. Re: VDbench response time
              Henk Vandenbergh-Oracle

              It appears you are looking at detailed information about "the life of an i/o".

              That is completely outside of the scope of Vdbench.

              On Solaris I would point you to start looking at Dtrace to figure this out, I expect that AIX has similar tools.

               

              Henk.

              • 4. Re: VDbench response time
                1010552

                Henk,

                 

                Thanks again for the reply. One more question:

                 

                In my case vdbench 'sd#.html' files show response time for each collection interval (5 sec) as around 4.5 ms. I am also collecting "nmon" which shows service time for respective disks as around 0.2 ms. Could you tell the command that Vdbench uses capture response time of an I/O.

                 

                Thanks.

                • 5. Re: VDbench response time
                  Henk Vandenbergh-Oracle

                  Please see my earlier reply:

                  "Since Vdbench starts each i/o itself, it knows when the i/o starts and when the i/o completes. The difference of these two equals the response time."


                  For AIX Vdbench uses gettimeofday().

                   

                  Henk.

                  • 6. Re: VDbench response time
                    1010552

                    Hi Henk,

                     

                    Thanks for the reply.

                     

                    I opened this discussion since I was seeing some abnormal response time for a workload with VDbench. Some details about this issue is as below:

                     

                    1. Initially (When I opened this discussion), I was using VDbench v5.02 with J2RE 1.5.0. The response time was around 5 ms for the workload.

                    2. Few days ago I used VDbench v5.04 with JRE 1.7.0 (nothing else was changed in the setup). The response time came down to 1.5ms for the same workload.

                    3. I used IORATE to generate the same workload which shows .5 ms.

                     

                    Ttherefore I guess this is an issue with VDbench's reporting about the I/O response time. Just want to understand how I may understand why Vdbench reports a higher response time. Please let me know if you need any other information.

                     

                    Thanks.