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[linux-lvm] Avoiding disk changes



Question regarding disk changes for LVMs. Are there any known scenarios where the on disk information will change (automatically) after the device(s) are detected and probed by the system?

My scenario is, I want to plug my LVM drive(s) into a different machine (via external USB) for analysis. I want the drives to remain 100% unmodified.

I would like to setup my configuration such that no disk changes will occur. Does anything within the LVM or DM realm modify the on-disk metadata under normal circumstances, or if a corrupted/broken LVM scheme is detected (partial or bad disk, etc.)?

In an attempt to gain absolute control over the detection and mounting process, I've set the global configuration file to test mode:

/etc/lvm/lvm.conf:
...
global {
...
	test = 1
...


After that, once I plug my device in, I set the LVM_SYSTEM_DIR env variable to point to my own configuration (because I don't want to twiddle with the system-wide one anymore than I have to).

I then use "vgchange --partial -a y" to access the new device, and create the /dev nodes.

In my custom lvm.conf (located in the $LVM_SYSTEM_DIR) I've set a few paranoid settings, including:

	filter = ... (only accept /dev/sd* devices)
	write_cache_state = 0
	backup = 0
	archive = 0
	locking_type = 0

Setting test mode in this configuration wasn't allowing me to do the vgchange, so I left that off.

Hope this isn't too open ended of a question, short if diving into the source code, I've tried to research to what extent LVM might automatically twiddle bits on the drive.

Thanks in advance.


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