Re: os io unit , db block size relation

Hi Fabrizio ,Yong

Sorry for delay , it will take some time to complete the other jobs. Based on your comments and tests , i made some tests against ocfs so i believe this time each time i read data from disk no caching is occurred.

This is iostat output:

avg-cpu: %user %nice %sys %idle

         260.95 0.00 3.90 759.15

Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz avgqu-sz await svctm %util

sde      6360.80  37.20 145.60  3.20 6542.40   40.40  
 44.24     1.25    8.41   2.31  35.26

While your tests show great difference between rrqm/s and rsec/s or wrqm/s and wsec/s , here these values are very close to each other.

Why dont we use r/s or w/s ?

Kind Regards,
tolga

FM <fabrizio.magni_at_mycontinent.com> wrote in message news:<k3n2d.264052$OR2.11933243_at_news3.tin.it>...
> I'm still waiting for a reply from Godard but reviewing your math and
> the result you posted I'm starting to believe caching has nothing to do
> with the missing bytes.
>
> What if the metrics are average on seconds?
>
> The time period of your iostat is 5 seconds.
> So:
>
> 5526.00 (sectors per second) * 512 (bytes) * 5 (seconds)= 14146560 (bytes)
>
> Now you have to understand whre 3660800 bytes come from.
> Were you using the device for other porpuses?
>
> Fabrizio
>
>
> utkanbir wrote:
>
> > Hi Fabrizio,
> >
> > Thank you very much for your help.
> >
> > I have made a small test:
> >
> > [oracle_at_tanidw1 tolga]$ time strace -T dd
> > if=/oracle/ett/data/current/tanduyurus
> > ure.txt of=/dev/null bs=10485760 count=5
> >
> > Here i try to read 5 10MB. blocks from a file which is stored in ext3
> > file system.The file system is also part of raid10 array which is EMC
> > . We use 960kb. of stripe size and have one io channel.
> >
> > Before running this command , i execute iostat -x /dev/sdm1 20 on
> > another terminal .
> >
> > Here is the strace output :
> >
> > read(0, "DUYURU_KOD|UYE_ISYERI_KOD|SUBE_K"..., 10485760) = 10485760
> > <0.594360>
> > write(1, "DUYURU_KOD|UYE_ISYERI_KOD|SUBE_K"..., 10485760) = 10485760
> > <0.000008>
> > read(0, "42\n3133|2|33|485|20040914000000|"..., 10485760) = 10485760
> > <0.409270>
> > write(1, "42\n3133|2|33|485|20040914000000|"..., 10485760) = 10485760
> > <0.000012>
> > read(0, "1508|20040914000000|094029|8|1|1"..., 10485760) = 10485760
> > <0.462430>
> > write(1, "1508|20040914000000|094029|8|1|1"..., 10485760) = 10485760
> > <0.000012>
> > read(0, "124457\n896|497|1|3352|2004091400"..., 10485760) = 10485760
> > <0.437568>
> > write(1, "124457\n896|497|1|3352|2004091400"..., 10485760) = 10485760
> > <0.000013>
> > read(0, "1|2|99|1054|20040914000000|17451"..., 10485760) = 10485760
> > <0.317013>
> > write(1, "1|2|99|1054|20040914000000|17451"..., 10485760) = 10485760
> > <0.000008>
> > munmap(0x2000000000308000, 10534912) = 0 <0.000611>
> >
> > real 0m3.075s
> > user 0m0.006s
> > sys 0m0.088s
> >
> > And , iostat values :
> >
> > avg-cpu: %user %nice %sys %idle
> > 253.93 0.00 12.25 757.83
> >
> > Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz avgqu-sz
> > await svctm %util
> > sdm1 590.70 0.05 100.05 0.40 5526.00 3.60 55.05 6.81
> > 67.80 1.51 15.53
> >
> >
> > It is clear that the dd command reads 50MB. I want to see this in
> > iostat command :
> >
> > iostat says 5526.00 sectors are read. So this is 2763 KB.
> > (5526*521bytes )
> >
> > I dont know which part i missed? (May be i forgot the simple math !)
Received on Thu Sep 30 2004 - 00:56:54 CDT