Dne 9.3.2017 v 12:24 Gionatan Danti napsal(a):
On 08/03/2017 19:55, Zdenek Kabelac wrote:
Hi
If you do NOT specify any setting - lvm2 targets 128M metadata size.
If you specify '--chunksize' lvm2 tries to find better fit and it happens
to be slightly better with 256M metadata size.
Basically - you could specify anything to the last bit - and if you
don't lvm2 does a little 'magic' and tries to come with 'reasonable'
defaults for given kernel and time.
That said - I've in my git tree some rework of this code - mainly for
better support of metadata profiles.
(And my git calculation gives me 256K chunksize + 128M metadata size -
so there was possibly something not completely right in version 166)
256 KB chunksize would be perfectly reasonable
Why I saw two very different metadata volume sizes? Chunksize was 128
KB in
both cases; the only difference is that I explicitly specified it on the
command line...
You should NOT forget - that using 'thin-pool' without any monitoring
and automatic resize is somewhat 'dangerous'.
True, but I should have no problem if not using snapshot or overprovisioning -
ie when all data chunks are allocated (filesystem full) but no
overprovisioned. This time, however, the created metadata pool was
*insufficient* to even address the provisioned data chunks.
Hmm - it would be interesting to see your 'metadata' - it should be still
quite good fit 128M of metadata for 512G when you are not using snapshots.
What's been your actual test scenario ?? (Lots of LVs??)
But as said - there is no guarantee of the size to fit for any possible use
case - user is supposed to understand what kind of technology he is using,
and when he 'opt-out' from automatic resize - he needs to deploy his own
monitoring.
Otherwise you would have to simply always create 16G metadata LV if you do not
want to run out of metadata space.
I am under impression that 128 KB size was chosen because this was MD chunk
size. Indeed further tests seem to confirm this.
Ahh yeah - there was small issue - when the 'hint' for device geometry was
used it has started from 'default' 64K size - instead of already counted 256K
chunk size.
Regards
Zdenek
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