[DRBD-user] [Testing issue] How to destroy meta-data of DRBD devices between the cluster?

Christian Iversen chrivers at iversen-net.dk
Mon Mar 8 16:57:57 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 2010-03-08 16:39, leishou yu wrote:
> Hi friends,
> Our product is running on a cluster system where SLES 10.2 and DRBD
> 0.7.24 are installed. The DRBD device is built upon the physical disk
> partition */dev/sda5*  and business data is written to and read from the
> DRBD device.
> As I have observed, there is an inconsistency of DRBDs at the first time
> when the cluster join each other. According to the DRBD manual, we need
> to execute "*drbdadm -- --do-what-I-say primary all*" to force one node
> of the cluster into primary.
> For testing reason I need to reinstall (again and again) the cluster
> system with the current hardware and software configuration. The
> reinstallation include disk partitioning and disk formatting with
> reiserfs. After the reinstallation, I will run the DRBD application
> and I hope to see the inconsistency of DRBD as described above. But I
> failed.
> As I guess, although the physical disk partition is re-formated, the
> content of the disk partition */dev/sda5*  has not been changed and  the
> meta-data of DRBD devices is  also not destroyed. When the DRBD devices
> get connected again, they recognized the *old valid information *and
> won't be inconsistent.
> Am I right?
> So my question is: *How to destroy meta-data of DRBD devices between the
> cluster? B*y destroying the meta-data, the disk partition is "rolled back".
> Someone introduced the *dd* tool which can full the disk partition
> */dev/sda5**. But I wonder there is some method more efficient.*
> *
> *
> *Thanks for help!*

Well, if I'm not mistaken, "internal" metadata is stored at the end of 
partitions. Thus, you can use the "dd_rescue" tool in "reverse" mode 
(which writes from the end instead of the start), to null the last 200MB:

dd_rescue -r -m 200M /dev/zero /dev/sda5

This is untested, but might just work. It should only take 5 minutes to try.

Oh, by the way, the disk has not been formatted if the metadata is still 
there. Formatting implies clearing the data on the block device. Maybe 
you have written a new filesystem with mkfs?

Med venlig hilsen
Christian Iversen

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