[DRBD-user] dual primary mode with which FS

[Stefan Seifert]

On Tuesday 23 March 2010 22:57:39 Christian Iversen wrote:

> Well, there's that. But the *primary* can't change anything either! Data
> would change while the filesystem expects it not to. Even if you somehow
> disable all caching (which you can't do without changing the kernel),
> you would STILL get serious data corruption errors, because of the many
> possible race conditions.
> 
> > It's not wise, but it's not impossible, either.
> 
> It is impossible, though. Unless NEITHER node ever change the data. And
> in that case, you might as well just copy it out once and for all.

If one really wants to read on the secondary there's an easy way: put DRBD on 
top of LVM and create a snapshot and mount that ro. Works just as one would 
expect including the absolutely obvious side effects of working with a 
snapshot like having to recreate it to get updated data. And even the sysadmin 
two generations from now will immediately understand this.

Regards,
Stefan