[DRBD-user] data integrity in drbd

Arnold Krille arnold at arnoldarts.de
Fri Aug 26 19:27:37 CEST 2011

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

On Friday 26 August 2011 17:33:09 Lyre wrote:
> Yesterday,  On the secondary,  I shut down drbd, try to use rsync to
> recovery the snapshot, but failed. Then I start drbd to resync from the
> primary node. It was the only time I bypass drbd, howerver,the application
> seems good at that time.
> This afternoon, we continue our experiment, disconnect drbd on secondary,
> changed something and resync from priamry.  Oracle was unable to start.
> drbd status suggest that both node were uptodate, drbadm verify doesn't
> report any error. Disconnect one side and mount drbd device on both node,
> md5sum show that some files were different.

rsync works on file(-system)-level, drbd compares disks and blocks. So by 
mixing both these tools, even though the filesystem mounted by hand on both 
seems to be the same, the disks aren't the same anymore once rsync did write 
And during the time drbd is off and you changed something, drbd will not 
recognize these changes. Due to the fact that a) drbd was off at that time and 
b) drbd works on block-device-level.

If this sounds like "you are fu**ed", that is partly intended. Mixing the 
levels of access is experimental at best and you better have a backup before 
starting such stuff.

Have fun,

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