[linux-lvm] lvm metadata sequence number reverts

Aaron Young aaron.young at ctl.io
Tue Sep 15 21:18:18 UTC 2015

Hello, I'm deep into debugging an issue we have with a disk driver of ours
and LVM.

Long story short:

create vg -> seqno 1
create lv1 -> seqno 2
create lv2 -> seqno 3
create lv3 -> seqno 4
create lv4 -> seqno 5
<clear our device cache> (note, this generates no IO)
vgdisplay: seqno = 4, lv4 is missing

* This happens only after dozens to hundreds of iterations. Most of the
time it is fine.

I dd all the metadata blocks off of the pv, yep, seqno5 is on disk metadata
area perfectly fine. But the system believes 4 is the current version.
Shouldn't the system be using the highest value? Or is it stored somewhere?
What mechanism is responsible for changing the seqno? And where does it
change it? (Not the metadata contents, just the number)


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