[Nbd] 答复: 答复: NBD io request size is always 4KB on Centos6.4

It works. Thank you Paul!

发件人: Paul Clements [mailto:paul.clements@...856...]
发送时间: 2014年2月15日 4:57
收件人: 刘海锋
抄送: nbd-general@lists.sourceforge.net
主题: Re: [Nbd] 答复: NBD io request size is always 4KB on Centos6.4

Hi,

do you have the rotational flag set on the nbd block device? If not, try setting that to enable the IO request elevator to merge requests.

Paul

On Wed, Feb 12, 2014 at 10:49 PM, 刘海锋 <bjliuhaifeng@...1493...> wrote:

Iostat as below:

Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz avgqu-sz await svctm %util
sda 0.00 564.67 0.00 53.33 0.00 4944.00 92.70 0.03 0.47 0.15 0.80
nb0 0.00 0.00 0.00 8765.33 0.00 70122.67 8.00 144.72 16.48 0.11 100.00

Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz avgqu-sz await svctm %util
sda 0.00 585.33 0.00 51.00 0.00 5090.67 99.82 0.02 0.48 0.16 0.80
nb0 0.00 0.00 0.00 8716.67 0.00 69733.33 8.00 145.14 16.64 0.11 99.97

Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz avgqu-sz await svctm %util
sda 0.00 561.33 0.00 50.67 0.00 4896.00 96.63 0.01 0.24 0.09 0.47
nb0 0.00 0.00 0.00 8815.00 0.00 70520.00 8.00 145.25 16.51 0.11 100.00

In contrast to Centos64, the official kernel 2.6.32 doesn’t have this problem ?C it merges io requests into 100+ kB.

发件人: 刘海锋 [mailto:bjliuhaifeng@...1493...]
发送时间: 2014年2月13日 11:44
收件人: 'nbd-general@lists.sourceforge.net'
主题: NBD io request size is always 4KB on Centos6.4

Dear nbd maintainers/users,

Recently we found an annoying case: iostat shows the read/write IO requests from nbd are very small (always 4kB exactly without any merges) on Centos64.

And we tried tuning various kernel parameters but failed to solve it. Any suggestions?

Thank you all.

--haifeng

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