[DRBD-user] c-min-rate priority

Ben RUBSON ben.rubson at gmail.com
Mon May 25 11:50:37 CEST 2015

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.

The link between nodes is a 10Gb/s link.
The DRBD resource is a RAID-10 array which is able to resync at up to 800M (as you can see I have lowered it to 680M in my configuration file).

The "issue" here seems to be a prioritization "issue" between application IOs and resync IOs.
Perhaps I miss-configured something ?
Goal is to have resync rate up to 680M, with a minimum of 400M, even if there are application IOs.
This in order to be sure to complete the resync even if there are a lot of write IOs from the application.

With my simple test below, this is not the case, dd still writes at its best throughput, lowering resync rate which can’t reach 400M at all.

Thank you !

> Le 25 mai 2015 à 11:18, A.Rubio <aurusa at etsii.upv.es> a écrit :
> the link between nodes is ???  1Gb/s ??? , 10Gb/s ??? ...
> the Hard Disks are ??? SATA 7200rpm ???, 10000rpm ???, SAS ???,
> SSD ???...
> 400M to 680M with a 10Gb/s link and SAS 15.000 rpm is OK but less ...
> El dom, 24-05-2015 a las 20:43 +0200, Ben RUBSON escribió:
>>> Le 12 avr. 2014 à 17:23, Ben RUBSON <ben.rubson at gmail.com> a écrit :
>>> Hello,
>>> Let's assume the following configuration :
>>> disk {
>>>    c-plan-ahead 0;
>>>    resync-rate 680M;
>>>    c-min-rate 400M;
>>> }
>>> Both nodes are uptodate, and on the primary, I have a test IO burst running, using dd.
>>> I then cut replication link for a few minutes so that secondary node will be several GB behind primary node.
>>> I then re-enable replication link.
>>> What I expect here according to the configuration is that secondary node will fetch missing GB at a 400 MB/s throughput.
>>> DRBD should then prefer resync IOs over application (dd here) IOs.
>>> However, it does not seems to work.
>>> dd still writes at its best throughput, meanwhile reads are made from the primary disk between 30 and 60 MB/s to complete the resync.
>>> Of course this is not the expected behaviour.
>>> Did I miss something ?
>> Hello,
>> Could I have your feedback please regarding this ?
>> Thank you !
>> Ben

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