Dne 23. 06. 20 v 16:26 Vojtech Juranek napsal(a):
Hi,
I'm working on storage part of oVirt project [1]. Besides other options, we
provide iSCSI storage for VMs. We create PV(s) on attached LUN(s), create
volume group from this PV(s) and then create LVs on this VG as needed (each
disk on its LV, similar there's dedicated LV for our metadata etc.). VG is
what we call (block) storage domain.
When we remove storage domain we deactivate all LVs and remove LVs and VG from
all hosts. However, when this fails (e.g. storage is for some reason
unavailable), hosts are left with stale LVs and VG which can cause various
issues for us. What we are going to do is to remove these stale VG mappings
using dmsetup remove command (first we try to remove LVs using lvm, but if
there are still some mappings, we will try to remove it using dmsetup).
I'd like to head your opinion on this approach. Is it wise to use dmsetup in
such case? Or is there any better way how to handle such situations or remove
stale mappings?
Hi
Of course you can remove 'stale' mapping with 'dmsetup remove' -
(after all lvm2 is doing basically very similar job like
'dmsetup create/remove/load/suspend/resume'....
BUT I'd probably focus rather on fixing your oVirt workflow - you should
not be 'losing' devices while you have activate mappings on them - that's
IMHO major desing flaw - you can very easily cause very SERIOUS damages
to your on disk data consistency - so disk would require serious fsck before
reuse...
Note - you cannot 'remove' mappings 'in-use' (aka open count of a device
is higher then 0 - see 'dmsetup info -c' output for this).
However you can replace such mapping with 'error' target - so the
underlaying device is relaxed - although we do not support this
in lvm2 - you would need to use 'dmsetup' for this (and open lvm2 RFE
if there would be some serious justifaction).
Regards
Zdenek
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