[DRBD-user] Build a DRBD partition without clean old data

Michael Haverkamp mhaverkamp at kcp.com
Tue Mar 8 15:36:52 CET 2005

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

Longming Lee wrote:
> Hi,
> I prepare two PCs for DRBD and duplicate /dev/sdb1 to each other by DRBD.
> But there are some data in PC1 /dev/sdb1 already. I issued
> 'drbdsetup /dev/drbd0 primary --do-what-I-say' at both PCs, and don't
> do 'mkfs -t ext3 /dev/drbd0' at PC1 for keeping old data, but do it at PC2.
> Reboot both PC and start DRBD and Heartbeat OK. Data of /dev/drbd0 will be
> replicated from PC1 to PC2.
I don't understand what you are trying to say about having data on
/dev/sdb1 that you are trying to save, so I will ignore that in my
explanation below.

'drbdsetup /dev/drbd0 primary --do-what-I-say' should only be done on 1
system, and only right after you initially set up drbd0.  This will
cause the other system to do a full resync of data from the system you
just made primary.  Check /proc/drbd to see that this is happening.

Also, it probably would have been a good idea to let this resync
complete before you rebooted both boxes.

> But:
> 1. The disk I/O performance of /dev/drbd0 is very poor.
> 2. I disconnect the network of PC1, then I get the error message at PC1:
> "Kernel panic: drbd0: Sorry, I have no access to goot data anymore."
The likely explanation for both of these is that the "primary" system
does not have a local copy of the data on /dev/drbd0.  That will cause
the primary system to do all of its IO over the network, and when the
network goes down, it no longer has access to the data and panics.

This may have been cause by you rebooting both boxes before the initial
resync was completed (see above).

> If I do 'mkfs -t ext3 /dev/drbd0' at PC1, DRBD will be OK after I disconnect
> the network of PC1 and well done.
> How can I make a good /dev/drbd0(/dev/sdb1) without clear old data of
> /dev/drbd0?
> (/dev/sdb1 is the physical disk partition used)
>From reading everything else you sent, it sounds like you may have
already destroyed your data.  Either that your you explanation above was

> regards,
> Longming 3/8
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Michael Haverkamp

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