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Re: [linux-lvm] Missing error handling in lv_snapshot_remove



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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