drbd-user March 2010 archive
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drbd-user: Re: [DRBD-user] dual primary mode with which FS

Re: [DRBD-user] dual primary mode with which FS

From: Stefan Seifert <nine_at_nospam>
Date: Wed Mar 24 2010 - 07:05:16 GMT
To: drbd-user@lists.linbit.com

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
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