[DRBD-user] dual primary mode with which FS

Christian Iversen chrivers at iversen-net.dk
Wed Mar 24 09:50:44 CET 2010

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

On 2010-03-24 08:05, Stefan Seifert wrote:
> 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.

Are you sure that LVM can create the snapshot without updating the 
metadata on the device? Because that's not allowed.

Med venlig hilsen
Christian Iversen

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