Dne 30. 08. 20 v 20:01 Gionatan Danti napsal(a):
Il 2020-08-30 19:33 Zdenek Kabelac ha scritto:
For illustration for 12.000 LVs you need ~4MiB just store Ascii
metadata itself, and you need metadata space for keeping at least 2 of
them.
Hi Zdenek, are you speaking of classical LVM metadata, right?
Hi
Lvm2 has only ascii metadata (so basically what is stored in
/etc/lvm/archive is the same as in PV header metadata area -
just without spaces and some comments)
And while this is great for manual recovery, it's not
very efficient in storing larger number of LVs - there basically
some sort of DB attemp would likely be needed.
So far however there was no real worthy use case - so safety
for recovery scenarios wins ATM.
Handling of operations like 'vgremove' with so many LVs requires
signification amount of your CPU time.
Basically to stay within bounds - unless you have very good reasons
you should probably stay in range of low thousands to keep lvm2 performing
reasonably well.
What about thin vols? Can you suggest any practical limit with lvmthin?
Thin - just like any other LV takes some 'space' - so if you want
to go with higher amount - you need to specify bigger metadata areas
to be able to store such large lvm2 metadata.
There is probably not a big issue with lots of thin LVs in thin-pool as long
as user doesn't need to have them active at the same time. Due to a nature of
kernel metadata handling, the larger amount of active thin LVs from the same
thin-pool v1 may start to compete for the locking when allocating thin pool
chunks thus killing performance - so here is rather better to stay in some
'tens' of actively provisioning thin volumes when the 'performance' is factor.
Worth to note there is fixed strict limit of the ~16GiB maximum thin-pool
kernel metadata size - which surely can be exhausted - mapping holds info
about bTree mappings and sharing chunks between devices....
Zdenek
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