[DRBD-user] Hardware-recomendation needed

Maurits van de Lande M.vandeLande at VDL-Fittings.com
Tue Apr 3 12:28:20 CEST 2012

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

>What do the experts think: Should this be sufficient to get the perfomance of a single SATA-Disk without DRBD?

Probably not, nothing will.

I'm using drbd in primary/primary mode to host KVM images on a two node cluster. (with drbd8.3.12, drbd8.4.1 has some performance issues)
I have switched to SSD's myself(in raid 5 mode). This improved the VM performance, (I guess because reading data is much faster), but drbd syncer speed did not improve. I even installed a 10G network backbone and used 10G network adapters on the servers. But still syncer speed does not go beyond 110MB/s.

I let Linbit look at this setup but they could not get a higher syncer speed with protocol C. I think the problem is that the syncer uses a single thread and therefore is limited by the processing power of one cpu. Turning off power management and IRQ balance helped a little bit, but not much.

I have spend ages trying to increase the syncer rate, for now it seems limited to 110MB/s. 

The is my latest drbd.conf 

# You can find an example in  /usr/share/doc/drbd.../drbd.conf.example

#include "drbd.d/global_common.conf";
#include "drbd.d/*.res";

# please have a a look at the example configuration file in
# /usr/share/doc/drbd83/drbd.conf

global {
    minor-count 64;
    usage-count yes;

common {
  syncer { 
  rate 110M;
  verify-alg crc32c;
  #csums-alg sha1; # do not use, slow performance
  al-extents 3733;
  cpu-mask 3;

resource VMstore1 {

  protocol C;

  startup {
    wfc-timeout  1800; # 30 min
    degr-wfc-timeout 120;    # 2 minutes.
    become-primary-on both;

  disk {

  net {
    max-buffers 8000;
    max-epoch-size 8000;
    sndbuf-size 0;
    after-sb-0pri discard-zero-changes;
    after-sb-1pri discard-secondary;
    after-sb-2pri disconnect;
    cpu-mask 3;

 on vmhost6a.vdl-fittings.local {
    device     /dev/drbd0;
    disk       /dev/sdb1;
    meta-disk  internal;
 on vmhost6b.vdl-fittings.local {
    device    /dev/drbd0;
    disk       /dev/sdb1;
    meta-disk internal;

Best regards,

Maurits van de Lande

-----Oorspronkelijk bericht-----
Van: drbd-user-bounces at lists.linbit.com [mailto:drbd-user-bounces at lists.linbit.com] Namens Lukas Gradl
Verzonden: dinsdag 3 april 2012 11:54
Aan: drbd-user at lists.linbit.com
Onderwerp: Re: [DRBD-user] Hardware-recomendation needed

> I'm not sure I understand the question, sorry.
> DRBD isn't much slower than the native disk performance, provided your 
> network is fast enough. So the question is less about DRBD's 
> performance as it is about the performance you need from the storage. 
> If a standard SATA drive's performance is fine, then it's all you need.

I followed the discussion about switch or no switch.

But I'm still stuck with my questions...

For use with KVM with automatic failover I need a primary/primary setup, so AFAIK protocol C is required.

According to my benchmarks DRBD is much slower in that setup than native HDD performance and changing the Network-Setup from 1GBit direct link to
2 bonded interfaces doesn't increase speed.

As we've just space for one 3.5" HDD (the other bay is used by the
Boot-SSD) I'm unable to install a raid5-setup.

So I think about installing two SSDs per Server using a 2x2.5" to 1x3.5"
adapter and leaving 20% of each ssd's space unpartitioned because of the lack of TRIM support. 
Then I would create 2 DRBD devices, to store the KVM-Images onto.
Moneywise this is not cheap but ok with our budget.

What do the experts think: Should this be sufficient to get the perfomance of a single SATA-Disk without DRBD?


software security networks
Lukas Gradl <proxmox#ssn.at>
Eduard-Bodem-Gasse 6
A - 6020 Innsbruck
Tel: +43-512-214040-0
Fax: +43-512-214040-21

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