[linux-lvm] Avoiding disk changes
jward at idealcorp.com
Wed Oct 4 19:10:18 UTC 2006
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%
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:
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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