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Unable to rate limit synchronization traffic with DRBD

 

 

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singh.rahul.1983 at gmail

Jul 16, 2012, 7:53 AM

Post #1 of 3 (741 views)
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Unable to rate limit synchronization traffic with DRBD

Hi All,
I am a new user of DRBD. I am trying to use DRBD to send disk updates to a
backup disk at a configuration rate in an asynchronous manner. From the DRBD
documentation it looks like i should be able to do this if i use Protocol A.


But when i write a file onto the partition that is being backed up by DRBD i
continue to see that the network traffic is very high inspite of me setting
the sync rate.

Here is my /etc/drbd.d/global_common.conf
global {
usage-count yes;
}

common {
}

and /etc/drbd.d/r0.res
resource r0 {
protocol A;
syncer {
rate 1M;
}
on obelix27 {
device /dev/drbd1;
disk /dev/sda1;
address 192.168.245.27:7789;
meta-disk internal;
}
on obelix28 {
device /dev/drbd1;
disk /dev/sda1;
address 192.168.245.28:7789;
meta-disk internal;
}
}

I have ubuntu 11.10 with linux kernel 3.0.0-12-generic. I installed the
userland part of DRBD using apt-get which is version 8.3.

I have tried issuing the drbdadm syncer r0 command. I am writing data on the
partition using

dd if=/dev/zero of=/mnt/more/file.dat count=1024 bs=1048576 and i am
measuring the network traffic using ifstat. Inspite of my setting the sync
rate to 1MB i continue to see 10 MB traffic.

What am i doing wrong ?

Thanking you,
Rahul
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jsmith at argotec

Jul 16, 2012, 9:33 AM

Post #2 of 3 (710 views)
Permalink
Re: Unable to rate limit synchronization traffic with DRBD [In reply to]

----- Original Message -----
> From: "rahulcs" <singh.rahul.1983 [at] gmail>
> To: drbd-user [at] lists
> Sent: Monday, July 16, 2012 10:53:18 AM
> Subject: [DRBD-user] Unable to rate limit synchronization traffic with DRBD
>
>
> Hi All,
> I am a new user of DRBD. I am trying to use DRBD to send disk updates
> to a
> backup disk at a configuration rate in an asynchronous manner. From
> the DRBD
> documentation it looks like i should be able to do this if i use
> Protocol A.
>
>
> But when i write a file onto the partition that is being backed up by
> DRBD i
> continue to see that the network traffic is very high inspite of me
> setting
> the sync rate.
>
> Here is my /etc/drbd.d/global_common.conf
> global {
> usage-count yes;
> }
>
> common {
> }
>
> and /etc/drbd.d/r0.res
> resource r0 {
> protocol A;
> syncer {
> rate 1M;
> }
> on obelix27 {
> device /dev/drbd1;
> disk /dev/sda1;
> address 192.168.245.27:7789;
> meta-disk internal;
> }
> on obelix28 {
> device /dev/drbd1;
> disk /dev/sda1;
> address 192.168.245.28:7789;
> meta-disk internal;
> }
> }
>
> I have ubuntu 11.10 with linux kernel 3.0.0-12-generic. I installed
> the
> userland part of DRBD using apt-get which is version 8.3.
>
> I have tried issuing the drbdadm syncer r0 command. I am writing data
> on the
> partition using
>
> dd if=/dev/zero of=/mnt/more/file.dat count=1024 bs=1048576 and i am
> measuring the network traffic using ifstat. Inspite of my setting the
> sync
> rate to 1MB i continue to see 10 MB traffic.
>
> What am i doing wrong ?

Syncer rate will only limit the re-sync rate when one side is out of sync such as the initial sync when first creating the resource. Normal uptodate/uptodate operations is to send writes as fast as the network and I/O subsystems will allow.

HTH

Jake


arnold at arnoldarts

Jul 16, 2012, 9:36 AM

Post #3 of 3 (720 views)
Permalink
Re: Unable to rate limit synchronization traffic with DRBD [In reply to]

Hi,

On Monday 16 July 2012 07:53:18 rahulcs wrote:
> I am a new user of DRBD. I am trying to use DRBD to send disk updates to a
> backup disk at a configuration rate in an asynchronous manner. From the DRBD
> documentation it looks like i should be able to do this if i use Protocol
> A.
> But when i write a file onto the partition that is being backed up by DRBD i
> continue to see that the network traffic is very high inspite of me setting
> the sync rate.
<snip>
> What am i doing wrong ?

The sync-rate is for when drbd has detected that there is a difference between
the peers and it needs to sync these. For example after a downtime of the
secondary while the primary was used. Or when drbd checks its whole disks and
syncs the differences.
That is totally independent from the normal writes, which are done on the
secondary at the same time as on the primary. Even with protocol A!
The protocols only report different states as "written": While C only reports a
block as written after local and remote disk have actually written the data to
disk, A reports a block as written when the local disk is written and the same
data has left the local network-interface. Still all this gets written on the
secondary the same as on the primary.

When you want to limit the transport or have a small connection and need
something to buffer the write-requests, talk to linbit about drbd-proxy...

Have fun,

Arnold
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