Actual DRBD disk parameters for higher sync rates on Debian 9

[John N.]

Hello,

In the past with Debian 7 and Debian 8 I have been using the following custom DRBD parameters when initializing my ganeti cluster with "gnt-cluster init -D":

drbd:c-max-rate=102400,resync-rate=102400,net-custom='--max-buffers 8000 --max-epoch-size 8000'

Now that I am starting afresh with a new Debian 9 ganeti cluster I was wondering if these settings are still actual?

My new Debian 9 cluster is using SSD disks and uses 1 Gigabit ethernet interfaces with ganeti 2.15.2, DRBD 8.9.10 and Xen 4.8.3. Right now this new cluster has no such custom DRBD parameters applied so it is using the defaults and the DRBD sync rates are around top 30 MB/s.

Best regards,
John

[micah anderson]

"John N." <hosting...@gmail.com> writes:

> Hello,
>
> In the past with Debian 7 and Debian 8 I have been using the following
> custom DRBD parameters when initializing my ganeti cluster with
> "gnt-cluster init -D":
>
> drbd:c-max-rate=102400,resync-rate=102400,net-custom='--max-buffers 8000
> --max-epoch-size 8000'

What kind of switch are you dealing with?

I noticed that debian DSA's do the following[0]:

gnt-cluster modify -D drbd:net-custom="--max-buffers 36k --sndbuf-size 1024k --rcvbuf-size 2048k"
gnt-cluster modify -D drbd:c-min-rate=32768
gnt-cluster modify -D drbd:c-max-rate=98304
gnt-cluster modify -D drbd:resync-rate=98304

i'm not sure what size switches these are all oriented around either.

--
micah

0. https://dsa.debian.org/howto/install-ganeti/

[John N.]

On Wednesday, May 16, 2018 at 4:24:01 PM UTC+2, micah wrote:

 

What kind of switch are you dealing with?

The 3 nodes are whole attached to the same cisco nexus 2248tp 1gb ethernet switch with the default mtu (1500). 

 

I noticed that debian DSA's do the following[0]:

    gnt-cluster modify -D drbd:net-custom="--max-buffers 36k --sndbuf-size 1024k --rcvbuf-size 2048k"
    gnt-cluster modify -D drbd:c-min-rate=32768
    gnt-cluster modify -D drbd:c-max-rate=98304
    gnt-cluster modify -D drbd:resync-rate=98304

Nice one, I tried this out right now and the Debian SAs seem to have done a good job. With these settings DRBD syncs stably around 100 MB/s. It took a 2-3 minutes to ramp up from 40 MB/s to 100 MB/s but after it stayed until the end at the max sync rate.

Cheers,
J.