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From: Zdenek Kabelac <>
To: LVM general discussion and development <>,
	Gionatan Danti <>
Cc: "Tomas Dalebjörk" <>
Subject: Re: [linux-lvm] lvm limitations
Date: Sun, 30 Aug 2020 21:30:25 +0200	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

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?


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....


  reply	other threads:[~2020-08-30 19:30 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-29 23:25 [linux-lvm] lvm limitations Tomas Dalebjörk
2020-08-30 17:33 ` Zdenek Kabelac
2020-08-30 18:01   ` Gionatan Danti
2020-08-30 19:30     ` Zdenek Kabelac [this message]
2020-09-01 13:21       ` Gionatan Danti
2020-09-15 19:16         ` Tomas Dalebjörk
2020-09-15 20:08           ` Zdenek Kabelac
2020-09-15 21:24             ` Tomas Dalebjörk
2020-09-15 21:30               ` Stuart D Gathman
2020-09-15 22:24                 ` Gionatan Danti
2020-09-15 21:47               ` Zdenek Kabelac
2020-09-15 22:26                 ` Gionatan Danti
2020-09-16  4:25                   ` Tomas Dalebjörk
2020-09-17 19:24                     ` Zdenek Kabelac
2020-09-16  4:31                   ` Tomas Dalebjörk
2020-09-16  4:58                   ` Tomas Dalebjörk
2020-09-17 19:17                     ` Zdenek Kabelac
2020-09-17 19:32                   ` Zdenek Kabelac
2020-09-14  6:03 Tomas Dalebjörk

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