Dne 8.8.2013 15:33, Ritesh Raj Sarraf napsal(a):
Hello Zdenek,
On Wednesday 07 August 2013 02:43 PM, Zdenek Kabelac wrote:
You are breaking the lvm2 logic thus pushing the code to go
through unexpected error code path - user is never supposed to open
so called 'private' /dev/mapper/ devices.
Just checking if this applies to other device types of DM, or just LVM?
We recommend our users to rely on /dev/mapper/* Multipath Devices, as
_persistent_ ones.
We also recommend to pvcreate on top of /dev/mapper/* Multipath Devices.
multipath != lvm2
Multipath has its own rules how to use devices and make the available for use.
In lvm2 you could use lvm.conf preferred_names in this form:
preferred_names = [ "^/dev/mpath/", "^/dev/mapper/mpath", "^/dev/[hs]d" ]
But it's rather distro-specific how the multipath devices are made available
for the user - so the names above are mostly usable for RedHat distors
(I think Suse uses slightly different logic)
Note - using pvcreate on /dev/mapper is nothing against the lvm2 rule.
lvm2 rule is about supported device path for LVs - whenever you try to use
LV, you should always use '/dev/vgname/lvname' path.
So /dev/mapper/vgname-lvname is not supported way though it will work in
most cases - but i.e. one of the problems you may have is, that your tool
would need to properly handle '-' symbol here, other issue could be, that in
/dev/mapper you see a lot more devices i.e. all mirror legs and other so
called private devices which you could misuse for 'mount' and do a lot of
damage to internal metadata.
So the simple rule for LVs is to use /dev/vgname/lvname.
Zdenek
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