[tools] dstat shows incoherent disk transfers

[Dag Wieers]

On Fri, 21 Mar 2008, Carlos Carvalho wrote:

> I sampled with a period of 60s. Note that the lines are the averages
> because of --noupdate:
>
> duvel#~[ 8:07]  ~/dstat -d --noupdate -D total,md0,md4,md1,md2 60
> -dsk/total----dsk/md0-----dsk/md4-----dsk/md1-----dsk/md2--
> _read _writ:_read _writ:_read _writ:_read _writ:_read _writ
>  26M 1281k:  22M  436k: 751k  289k: 540B   25B: 128k   30k
>  36M 1166k:  34M  505k: 642k   54k:   0     0 : 819B   40k
>  39M 2136k:  37M  908k: 508k  133k:   0     0 :  14k   27k
>  39M 3533k:  33M 1964k: 501k   63k:   0     0 :  19k   46k
>  34M  848k:  33M  169k: 413k  110k:   0     0 :3345B   38k
>  36M 1420k:  34M  588k: 608k   47k:   0     0 :2389B   19k
>  35M 1927k:  33M  671k: 445k   48k:   0     0 :7851B   31k
>  37M 1574k:  35M  628k: 694k   47k:   0    68B: 341B   26k
>  34M 1550k:  33M  621k: 615k   72k:2321B    0 :  11k   17k
>  30M 1183k:  29M  325k: 381k   49k:   0     0 :3482B   59k
>  30M 1343k:  28M  478k: 417k   40k:  12k  324B: 478B   42k
>  30M  674k:  29M  146k: 756k   38k:   0   154B: 819B   31k
>  31M  569k:  30M  137k: 544k   35k: 137B  154B: 410B   47k
>  32M  620k:  31M  137k: 439k   39k:   0   137B:2253B   46k
>  30M  539k:  29M   68k: 803k   46k:   0    68B: 614B   63k
>  30M  773k:  29M  173k: 475k  111k:   0     0 : 410B   24k
>  28M  602k:  27M  137k: 626k   63k:   0     0 : 410B   35k
>  29M  547k:  29M   69k: 232k   49k:   0     0 : 137B   31k
>  27M  851k:  26M  250k: 329k   81k:1092B    0 : 137B   17k
>  26M 1048k:  25M  367k: 534k   86k:   0     0 :   0    27k
>  28M 1145k:  27M  526k: 373k   64k:   0     0 :   0    13k
>  30M 1023k:  29M  445k: 579k   55k:   0     0 : 683B   40k
>  27M  696k:  27M  137k: 318k   72k:   0     0 :  68B   63k
>  27M  948k:  26M  292k: 355k   68k: 273B    0 :  21k   54k
>  28M 1278k:  27M  551k: 441k   42k:   0     0 :7236B   34k
>  30M 2749k:  28M 1535k: 301k  118k:   0     0 : 205B   40k
>  30M 2948k:  26M 1510k: 549k   65k:   0     0 :  12k   20k
>  33M 3586k:  28M 1783k: 544k   77k:   0     0 : 410B   35k
>  32M 2686k:  29M 1408k: 427k   47k:   0     0 : 410B   32k
>  33M 4269k:  27M 2392k: 410k  122k:   0     0 : 887B   16k
>  31M 2640k:  28M 1424k: 456k   46k:   0     0 : 478B   28k
>  33M 3735k:  28M 2020k: 353k   61k:   0     0 : 137B   43k
>  33M 3505k:  28M 1743k: 360k   64k: 205B    0 :  16k   31k
>  36M 4071k:  30M 2175k: 392k   64k: 273B    0 : 205B   40k
>  32M 3194k:  26M 1563k: 342k   82k:   0     0 :3004B   26k
>  33M 3910k:  28M 2075k: 208k   81k:   0     0 :1911B   47k
>  32M 3140k:  27M 1450k: 361k   93k:   0     0 :  19k   40k
>  37M 3781k:  31M 2012k: 387k   55k:   0     0 : 205B   42k
>  35M 3401k:  30M 1725k: 346k   72k: 614B    0 :1707B   35k
>  35M 3896k:  31M 2173k: 215k   72k:   0     0 :5188B   24k
>  34M 2835k:  30M 1584k: 454k   87k:   0     0 : 137B   30k
>  36M 3539k:  30M 1555k: 604k   81k:   0     0 : 137B   15k
>  35M 2817k:  30M 1152k: 718k   72k:   0     0 :1775B   32k
>  35M 2500k:  30M  878k: 353k  112k:   0     0 :5871B   14k
>  34M 2360k:  31M 1100k: 393k   86k:   0     0 : 751B   60k
>  32M 1774k:  30M  829k: 285k   58k:   0     0 : 273B   26k
>  36M 3761k:  30M 1554k: 330k   54k:   0     0 : 273B   31k
>  36M 3447k:  30M 1236k:  96k   82k:   0     0 : 341B   59k
>  37M 3177k:  31M 1191k: 248k   78k: 546B    0 : 137B   27k
>  31M 2436k:  26M  924k: 324k   59k:   0     0 :3072B   44k
>  30M 1064k:  29M  316k: 320k   58k:   0     0 :  68B   47k
>  27M  984k:  26M  406k:  89k   79k:   0     0 :   0    25k
>  27M  760k:  26M  211k: 285k   71k:   0     0 : 205B   35k
>  30M  957k:  29M  414k: 449k   50k: 273B    0 :4983B   36k
>  39M 1244k:  38M  581k: 272k   64k:   0     0 : 137B   18k
>  35M 3719k:  34M  361k: 445k 1107k:  68B    0 : 683B   28k
>
> It's seen that the read figures are reasonable, no more total > md-disk.
> However the writes are consistently much higher the sum, by a factor
> of 2-3. This is hard to accept... Anybody else sees this?

I am not sure if you understood me well when I said that the total is the 
total from the physical devices excluding the md devices. We do this 
because otherwise we would be counting the same I/O twice.

If you have other disks in the system that are doing something the total 
would include that as well. The total is *not* the total of the selected 
disks.

-- 
--   dag wieers,  dag at wieers.com,  http://dag.wieers.com/   --
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