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Re: [linux-lvm] Is cLVM necessary when accessing different logical volumes on a shared iSCSI target?



>>  1) edit lvm.conf and disable all metadata caching

> 
> I have searched the lvm documentation, but could not find anything about 
> metadata caching.

write_cache_state = 0
use_lvmetad = 0


I also move the cache_dir out of /etc to a ephemeral location. /var/lock is tmpfs on my machines.
cache_dir = "/var/lock/subsys"


>>  2) edit lvm.conf and set the locking style to '4' and set 
> wait_for_locks=0
> 
> The clients have a local volume group besides the shared one. Setting the 
> locking style to 4 prevents
> modification of this local volume group, too, so it does not seem to be an 
> option.


You need 2 different lvm.conf's. Use the filter directive so that one can only see the local devices, and the other one only the shared devices.

filter = [ "a|local_devices|", ... "r|shared_devices" ]

vs
filter = [ "a|shared_devices|", ... "r|local_devices" ]

Run pvscan and pvs and make sure the exclusions are happening correctly.

> Each LV is statically assigned to one single host.


That's an important distinction! You can use just a single lvm.conf and a well crafted volume_list. I haven't played with tags but that might be rather useful as well.


volume_list = [ "vglocal", "vg_shared/lv_mine", "@mytag1" ]


> As I tried to describe above, the hosts do not behave as master or slave. 


Nevermind then. I was implementing a full-on Active/Active storage head that could take over each other's volumes at will.

> Is this possible with or without cLVM?

without.



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