[linux-lvm] dev node change

[Peter Rajnoha]

On 12/10/2013 03:33 PM, Alessandro MACUZ wrote:
> 2013/12/10 Peter Rajnoha <prajnoha at redhat.com <mailto:prajnoha at redhat.com>>
> 
>     On 12/09/2013 04:13 PM, Umar Draz wrote:
>     > Hi All
>     >
>     > I have a SCSI share which i am  using linux initiator on my
>     ubuntu. Its
>     > available for me in /dev/sdb
>     >
>     > No I have created lvm group using the /dev/sdb. Today I just logut and
>     > login my scsi share but this time ubutnu gave me this as /dev/sdc
>     > instead of /dev/sdb.
>     >
>     > due to this my lvm group is stuck, and its giving me the error
>     >
>     > Input/output error
>     >
>     > on pvdisplay or vgdisplay,
>     >
>     > Any body help me how I can reslove this issue.?
>     >
> 
>     You should always deactivate your LVM volumes before
>     disconnecting the underlying iSCSI volumes and then when
>     you reconnect the iSCSI back, activate the LVM volumes
>     (or if autoactivation is used - meaning use_lvmetad=1
>     is set in lvm.conf, this activation happens automatically).
> 
>     Alternatively, you can call vgchange --refresh when the
>     iSCSI is connected back.
> 
> 
> 
> Couldn't be used the identification of PV by UUID here? It should be
> better imo.
> 

Well, this is about dm tables that represent the logical volumes
(you can check dmsetup table output). The PV UUID doesn't play a role
at this level - the PV UUID is just LVM abstraction that is using
device-mapper kernel capabilities.

And if the iSCSI is disconnected while there's anything on top of it
(in this case the LV), the major:minor pair (as well as the kernel name)
is reserved until all the stack above it is freed.

Then when the iSCSI is connected back (while the old major:minor is
still held by old mapping), kernel has no other choice just to assign
new major:minor pair. Therefore we need a refresh (or deactivation/activation)
which will generate a new mapping with the new major:minor pair of the
underlying PV (the iSCSI volume).
-- 
Peter