[DRBD-user] slow disk throughput (fwd)

Tom Brown wc-linbit.com at vmail.baremetal.com
Tue Jun 17 21:37:06 CEST 2008

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

On Tue, 17 Jun 2008, William Francis wrote:

>  I upgraded my drbd kernel module and userland tools to 8.0.12 and added the
>  two additional parameters to my disk section of my drbd.conf as Lee
>  suggested and wow, a full 10X improvement in write speed, which is about 60%
>  of bare metal speed.
>  What does this suggest? Does 8.0.11 have some performance ....um, issues (or

(my bad, I sent this from an unsubscribed address, hopefully it will not 
show up twice...)

this has all been covered on the list...

     Date: Sat, 24 May 2008 21:35:10 +0200
     From: Philipp Reisner <philipp.reisner at linbit.com>
     To: drbd-user at linbit.com
     Subject: Re: [DRBD-user] 8.x performance vs 0.7x --- was (not urgent)
     Request for DRBD Developers

    > > >  Personally, I'm still on 8.0.8. Later versions at the time seemed to
    > > >  show _VASTLY_ reduced performance on my hardware, so I excluded it
    > > >  from
    > > >  the updates. I'm not experiencing any problems, so I'm sticking with
    > > >  it.

    That is due to that change:

     8.0.9 (api:86/proto:86)
      * In case our backing devices support write barriers and cache
        flushes, we use these means to ensure data integrity in
        the presence of volatile disk write caches and power outages.

     8.0.12 (api:86/proto:86)
      * Two new config options no-disk-flushes and no-md-flushes to disable
        the use of io subsystem flushes and barrier BIOs.

     But please *read* the documentation about "no-disk-flushes" and
     understand the implications before you set these options.

        #  In case you are sure that your storage subsystem has battery
        #  backed up RAM and you know from measurements that it really honors
        #  flush instructions by flushing data out from its non volatile
        #  write cache to disk, you have double security. You might then
        #  reduce this to single security by disabling disk flushes with
        #  this option. It might improve performance in this case.
        #  no-disk-flushes;
        #  no-md-flushes;

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