[DRBD-user] slow sync speed

Oleksiy Evin o.evin at onefc.com
Thu Oct 11 08:45:11 CEST 2018

You may try to disable dynamic sync rate by setting "c-plan-ahead" to 0 and increase "max-buffers". That's the only way which helped me to get reasonable sync rate with 100GigE connection.

net {
	max-buffers 32K;
	# max-epoch-size 18K;

disk {
	c-plan-ahead 0;

You can find some more info here: 


-----Original Message-----
From: Adam Weremczuk <adamw at matrixscience.com>
To: drbd-user at lists.linbit.com
Subject: [DRBD-user] slow sync speed
Date: Wed, 10 Oct 2018 14:57:02 +0100

Hi all,
I'm trying out DRBD Pacemaker HA Cluster on Proxmox 5.2
I have 2 identical servers connected with 2 x 1 Gbps links in bond_mode balance-rr.
The bond is working fine; I get a transfer rate of 150 MB/s with scp.
Following this guide: https://www.theurbanpenguin.com/drbd-pacemaker-ha-cluster-ubuntu-16-04/ was going  smoothly up until:
drbdadm -- --overwrite-data-of-peer primary r0/0
cat /proc/drbdversion: 8.4.10 (api:1/proto:86-101)srcversion: 17A0C3A0AF9492ED4B9A418  0: cs:SyncSource ro:Primary/Secondary ds:UpToDate/Inconsistent C r-----     ns:10944 nr:0 dw:0 dr:10992 al:8 bm:0 lo:0 pe:0 ua:0 ap:0 ep:1 wo:f oos:3898301536     [>....................] sync'ed:  0.1% (3806932/3806944)M     finish: 483:25:13 speed: 2,188 (2,188) K/sec
The transfer rate is horribly slow and at this pace it's going to take 20 days for two 4 TB volumes to sync!
That's almost 15 times slower comparing with the guide video (8:30): https://www.youtube.com/watch?v=WQGi8Nf0kVc
The volumes have been zeroed and contain no live data yet.
My sdb disks are logical drives (hardware RAID) set up as RAID50 with the defaults:
Strip size: 128 KBAccess policy: RWRead policy: NormalWrite policy: Write Back with BBUIO policy: DirectDrive Cache: DisableDisable BGI: No
Performance looks good when tested with hdparm:
hdparm -tT /dev/sdb1
/dev/sdb1:  Timing cached reads:   15056 MB in  1.99 seconds = 7550.46 MB/sec  Timing buffered disk reads: 2100 MB in  3.00 seconds = 699.81 MB/sec
The volumes have been zeroed and contain no live data yet.
It seems to be a problem with default DRBD settings.
Can anybody recommend optimal tweaks specific to my environment?
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