[DRBD-user] 8.x performance vs 0.7x --- was (not urgent) Request for DRBD Developers

Philipp Reisner philipp.reisner at linbit.com
Sat May 24 21:35:10 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.


[...]
> >>  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.
    # ONLY USE THIS OPTION IF YOU KNOW WHAT YOU ARE DOING.
    # no-disk-flushes;
    # no-md-flushes;

-Phil



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