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List:       drbd-user
Subject:    Re: after drbd down , is it safe to mount underlying device
From:       "Dingwall, James" <James.Dingwall () ncrvoyix ! com>
Date:       2024-04-16 7:15:43
Message-ID: BY3PR15MB5044C41F701F5546AB4BF8BAF7082 () BY3PR15MB5044 ! namprd15 ! prod ! outlook ! com
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> Small question regarding the underlying disk
> 
> If on the primary, and I started drbd on a disk with existing data,
> 
> some time later I unmount and I down drbd....
> 
> Can I directly mount the disk again without risk of corruption? or once drbd always \
> drbd?

This is safe so long as you don't write (if you intend to reform the DRBD resource) \
but beware even mounting some filesystems with `-o ro` can still result in writes.  \
You can add a generic step to prevent this by creating a loop device from the block \
device:

# losetup -Pfvr --show /dev/....

# ls /dev/loop1*
/dev/loop1  /dev/loop1p1  /dev/loop1p2

# mount /dev/loop1p2 /tmp/x
Error opening '/dev/loop1p2' read-write
Could not mount read-write, trying read-only

(That happened to be an NTFS formatted partition from a virtual machine)

If you do write to the disk and bypass drbd then you'll need to invalidate the \
secondary and resync.

James

=


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