iostat + how to solve latency on disks












0















we use iostat -x and check for the await column - per device it shows the total time spent waiting plus the actual handling of the request by the disk



iostat -yzx 5





Device:         rrqm/s   wrqm/s     r/s     w/s    rkB/s    wkB/s avgrq-sz avgqu-sz   await r_await w_await  svctm  %util

sdm               0.00     0.00    0.00    1.60     0.00     4.20     5.25     0.00    0.75    0.00    0.75   0.62   0.10

sda               0.00     0.40    0.00    3.00     0.00    24.70    16.47     0.11   37.60    0.00   37.60   7.13   2.14

sdc               0.00     0.00    0.00    0.80     0.00     6.10    15.25     0.01   12.75    0.00   12.75  12.75   1.02

sdb               0.00     0.00    0.00    0.40     0.00     2.40    12.00     0.01   19.50    0.00   19.50  19.50   0.78

sdd               0.00     0.00    0.00    0.80     0.00     6.60    16.50     0.01   10.75    0.00   10.75  10.75   0.86

sdg               0.00     0.00    0.00    1.00     0.00     8.90    17.80     0.02   15.80    0.00   15.80  15.80   1.58

sdf               0.00     0.20    0.00    1.00     0.00     8.00    16.00     0.01   12.80    0.00   82.80  12.80   1.28

sde               0.00     0.00    0.00    0.80     0.00     7.50    18.75     0.01   11.25    0.00   11.25  11.25   0.90

sdk               0.00     0.00    0.00    0.80     0.00     6.50    16.25     0.01   14.25    0.00   14.25  14.25   1.14

sdi               0.00     0.00    0.00    1.00     0.00     7.20    14.40     0.01   11.60    0.00   11.60  11.60   1.16

sdj               0.00     0.00    0.00    0.80     0.00     5.90    14.75     0.01   13.50    0.00   13.50  13.50   1.08

sdh               0.00     0.00    0.00    0.80     0.00     5.60    14.00     0.01   13.25    0.00   13.25  13.25   1.06

sdl               0.00     0.00    0.00    1.00     0.00     7.20    14.40     0.01   14.20    0.00   14.20  14.20   1.42

sdn               0.00     0.00    0.00    1.60     0.00     4.20     5.25     0.00    0.88    0.00    0.88   0.75   0.12

md1               0.00     0.00    0.00    0.40     0.00     3.20    16.00     

sdq               0.00     0.00    0.00    0.60     0.00     5.20    17.33     0.01   12.67    0.00   82.67  12.67   0.76

sdr               0.00     0.00    0.00    0.60     0.00     4.20    14.00     0.01   10.00    0.00   10.00  10.00   0.60


we can see from the output that await on some disk is high



my question - what we can do about this ?



any option to resolve this ?






linux hard-drive performance redhat-enterprise-linux io







share|improve this question



























    0















    we use iostat -x and check for the await column - per device it shows the total time spent waiting plus the actual handling of the request by the disk



    iostat -yzx 5
    

    

    
Device:         rrqm/s   wrqm/s     r/s     w/s    rkB/s    wkB/s avgrq-sz avgqu-sz   await r_await w_await  svctm  %util
    
sdm               0.00     0.00    0.00    1.60     0.00     4.20     5.25     0.00    0.75    0.00    0.75   0.62   0.10
    
sda               0.00     0.40    0.00    3.00     0.00    24.70    16.47     0.11   37.60    0.00   37.60   7.13   2.14
    
sdc               0.00     0.00    0.00    0.80     0.00     6.10    15.25     0.01   12.75    0.00   12.75  12.75   1.02
    
sdb               0.00     0.00    0.00    0.40     0.00     2.40    12.00     0.01   19.50    0.00   19.50  19.50   0.78
    
sdd               0.00     0.00    0.00    0.80     0.00     6.60    16.50     0.01   10.75    0.00   10.75  10.75   0.86
    
sdg               0.00     0.00    0.00    1.00     0.00     8.90    17.80     0.02   15.80    0.00   15.80  15.80   1.58
    
sdf               0.00     0.20    0.00    1.00     0.00     8.00    16.00     0.01   12.80    0.00   82.80  12.80   1.28
    
sde               0.00     0.00    0.00    0.80     0.00     7.50    18.75     0.01   11.25    0.00   11.25  11.25   0.90
    
sdk               0.00     0.00    0.00    0.80     0.00     6.50    16.25     0.01   14.25    0.00   14.25  14.25   1.14
    
sdi               0.00     0.00    0.00    1.00     0.00     7.20    14.40     0.01   11.60    0.00   11.60  11.60   1.16
    
sdj               0.00     0.00    0.00    0.80     0.00     5.90    14.75     0.01   13.50    0.00   13.50  13.50   1.08
    
sdh               0.00     0.00    0.00    0.80     0.00     5.60    14.00     0.01   13.25    0.00   13.25  13.25   1.06
    
sdl               0.00     0.00    0.00    1.00     0.00     7.20    14.40     0.01   14.20    0.00   14.20  14.20   1.42
    
sdn               0.00     0.00    0.00    1.60     0.00     4.20     5.25     0.00    0.88    0.00    0.88   0.75   0.12
    
md1               0.00     0.00    0.00    0.40     0.00     3.20    16.00     
    
sdq               0.00     0.00    0.00    0.60     0.00     5.20    17.33     0.01   12.67    0.00   82.67  12.67   0.76
    
sdr               0.00     0.00    0.00    0.60     0.00     4.20    14.00     0.01   10.00    0.00   10.00  10.00   0.60


    we can see from the output that await on some disk is high



    my question - what we can do about this ?



    any option to resolve this ?






    linux hard-drive performance redhat-enterprise-linux io







    share|improve this question

























      0












      0








      0








      we use iostat -x and check for the await column - per device it shows the total time spent waiting plus the actual handling of the request by the disk



      iostat -yzx 5
      

      

      
Device:         rrqm/s   wrqm/s     r/s     w/s    rkB/s    wkB/s avgrq-sz avgqu-sz   await r_await w_await  svctm  %util
      
sdm               0.00     0.00    0.00    1.60     0.00     4.20     5.25     0.00    0.75    0.00    0.75   0.62   0.10
      
sda               0.00     0.40    0.00    3.00     0.00    24.70    16.47     0.11   37.60    0.00   37.60   7.13   2.14
      
sdc               0.00     0.00    0.00    0.80     0.00     6.10    15.25     0.01   12.75    0.00   12.75  12.75   1.02
      
sdb               0.00     0.00    0.00    0.40     0.00     2.40    12.00     0.01   19.50    0.00   19.50  19.50   0.78
      
sdd               0.00     0.00    0.00    0.80     0.00     6.60    16.50     0.01   10.75    0.00   10.75  10.75   0.86
      
sdg               0.00     0.00    0.00    1.00     0.00     8.90    17.80     0.02   15.80    0.00   15.80  15.80   1.58
      
sdf               0.00     0.20    0.00    1.00     0.00     8.00    16.00     0.01   12.80    0.00   82.80  12.80   1.28
      
sde               0.00     0.00    0.00    0.80     0.00     7.50    18.75     0.01   11.25    0.00   11.25  11.25   0.90
      
sdk               0.00     0.00    0.00    0.80     0.00     6.50    16.25     0.01   14.25    0.00   14.25  14.25   1.14
      
sdi               0.00     0.00    0.00    1.00     0.00     7.20    14.40     0.01   11.60    0.00   11.60  11.60   1.16
      
sdj               0.00     0.00    0.00    0.80     0.00     5.90    14.75     0.01   13.50    0.00   13.50  13.50   1.08
      
sdh               0.00     0.00    0.00    0.80     0.00     5.60    14.00     0.01   13.25    0.00   13.25  13.25   1.06
      
sdl               0.00     0.00    0.00    1.00     0.00     7.20    14.40     0.01   14.20    0.00   14.20  14.20   1.42
      
sdn               0.00     0.00    0.00    1.60     0.00     4.20     5.25     0.00    0.88    0.00    0.88   0.75   0.12
      
md1               0.00     0.00    0.00    0.40     0.00     3.20    16.00     
      
sdq               0.00     0.00    0.00    0.60     0.00     5.20    17.33     0.01   12.67    0.00   82.67  12.67   0.76
      
sdr               0.00     0.00    0.00    0.60     0.00     4.20    14.00     0.01   10.00    0.00   10.00  10.00   0.60


      we can see from the output that await on some disk is high



      my question - what we can do about this ?



      any option to resolve this ?






      linux hard-drive performance redhat-enterprise-linux io







      share|improve this question














      we use iostat -x and check for the await column - per device it shows the total time spent waiting plus the actual handling of the request by the disk



      iostat -yzx 5
      

      

      
Device:         rrqm/s   wrqm/s     r/s     w/s    rkB/s    wkB/s avgrq-sz avgqu-sz   await r_await w_await  svctm  %util
      
sdm               0.00     0.00    0.00    1.60     0.00     4.20     5.25     0.00    0.75    0.00    0.75   0.62   0.10
      
sda               0.00     0.40    0.00    3.00     0.00    24.70    16.47     0.11   37.60    0.00   37.60   7.13   2.14
      
sdc               0.00     0.00    0.00    0.80     0.00     6.10    15.25     0.01   12.75    0.00   12.75  12.75   1.02
      
sdb               0.00     0.00    0.00    0.40     0.00     2.40    12.00     0.01   19.50    0.00   19.50  19.50   0.78
      
sdd               0.00     0.00    0.00    0.80     0.00     6.60    16.50     0.01   10.75    0.00   10.75  10.75   0.86
      
sdg               0.00     0.00    0.00    1.00     0.00     8.90    17.80     0.02   15.80    0.00   15.80  15.80   1.58
      
sdf               0.00     0.20    0.00    1.00     0.00     8.00    16.00     0.01   12.80    0.00   82.80  12.80   1.28
      
sde               0.00     0.00    0.00    0.80     0.00     7.50    18.75     0.01   11.25    0.00   11.25  11.25   0.90
      
sdk               0.00     0.00    0.00    0.80     0.00     6.50    16.25     0.01   14.25    0.00   14.25  14.25   1.14
      
sdi               0.00     0.00    0.00    1.00     0.00     7.20    14.40     0.01   11.60    0.00   11.60  11.60   1.16
      
sdj               0.00     0.00    0.00    0.80     0.00     5.90    14.75     0.01   13.50    0.00   13.50  13.50   1.08
      
sdh               0.00     0.00    0.00    0.80     0.00     5.60    14.00     0.01   13.25    0.00   13.25  13.25   1.06
      
sdl               0.00     0.00    0.00    1.00     0.00     7.20    14.40     0.01   14.20    0.00   14.20  14.20   1.42
      
sdn               0.00     0.00    0.00    1.60     0.00     4.20     5.25     0.00    0.88    0.00    0.88   0.75   0.12
      
md1               0.00     0.00    0.00    0.40     0.00     3.20    16.00     
      
sdq               0.00     0.00    0.00    0.60     0.00     5.20    17.33     0.01   12.67    0.00   82.67  12.67   0.76
      
sdr               0.00     0.00    0.00    0.60     0.00     4.20    14.00     0.01   10.00    0.00   10.00  10.00   0.60


      we can see from the output that await on some disk is high



      my question - what we can do about this ?



      any option to resolve this ?






      linux hard-drive performance redhat-enterprise-linux io




      linux hard-drive performance redhat-enterprise-linux io






      share|improve this question













      share|improve this question











      share|improve this question




      share|improve this question










      asked Jan 10 at 8:36









      King DavidKing David

      1931111




      1931111






















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          Your service times on the relevant disks are around 15ms - this is quite a normal value for spinning rust. Since you have only a very limited amount of outstanding I/O and nearly no reads, you are random write bound. Easiest way to resolve that is using bcache dm-cache or whatever with a decent SSD.






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            Your service times on the relevant disks are around 15ms - this is quite a normal value for spinning rust. Since you have only a very limited amount of outstanding I/O and nearly no reads, you are random write bound. Easiest way to resolve that is using bcache dm-cache or whatever with a decent SSD.






            share|improve this answer




























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              Your service times on the relevant disks are around 15ms - this is quite a normal value for spinning rust. Since you have only a very limited amount of outstanding I/O and nearly no reads, you are random write bound. Easiest way to resolve that is using bcache dm-cache or whatever with a decent SSD.






              share|improve this answer


























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                Your service times on the relevant disks are around 15ms - this is quite a normal value for spinning rust. Since you have only a very limited amount of outstanding I/O and nearly no reads, you are random write bound. Easiest way to resolve that is using bcache dm-cache or whatever with a decent SSD.






                share|improve this answer













                Your service times on the relevant disks are around 15ms - this is quite a normal value for spinning rust. Since you have only a very limited amount of outstanding I/O and nearly no reads, you are random write bound. Easiest way to resolve that is using bcache dm-cache or whatever with a decent SSD.







                share|improve this answer












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                answered Jan 10 at 8:44









                Eugen RieckEugen Rieck

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