On 27/03/2018 10:30, Zdenek Kabelac wrote:
Hi
Well just for the 1st. look - 116MB for metadata for 7.21TB is *VERY*
small size. I'm not sure what is the data 'chunk-size' - but you will
need to extend pool's metadata sooner or later considerably - I'd
suggest at least 2-4GB for this data size range.
Hi Zdenek,
as shown by the last lvs command, data chunk size is at 4MB. Data chunk
size and metadata volume size where automatically selected at thin pool
creation - ie: they are default values.
Indeed, running "thin_metadata_size -b4m -s7t -m1000 -um" show
"thin_metadata_size - 60.80 mebibytes estimated metadata area size"
Metadata itself are also allocated in some internal chunks - so
releasing a thin-volume doesn't necessarily free space in the whole
metadata chunks thus such chunk remains allocated and there is not a
more detailed free-space tracking as space in chunks is shared between
multiple thin volumes and is related to efficient storage of b-Trees...
Ok, so removing a snapshot/volume can free a lower than expected
metadata amount. I fully understand that. However, I saw the *reverse*:
removing a volume shrunk metadata (much) more than expected. This also
mean that snapshot creation and data writes on the main volume caused a
*much* larger than expected increase in metadata usage.
There is no 'direct' connection between releasing space in data and
metadata volume - so it's quite natural you will see different
percentage of free space after thin volume removal between those two
volumes.
I understand that if data is shared between two or more volumes,
deleting a volume will not change much from a metadata standpoint.
However, this is true for the data pool also: it will continue to show
the same utilization. After all, removing a shared volume only means
that data chunk are mapped in another volume.
However, I was under impression that a more or less direct connection
between allocated pool data chunk and metadata existed: otherwise, a
tool as thin_metadata_size lose its scope.
So, where am I wrong?
Thanks.
--
Danti Gionatan
Supporto Tecnico
Assyoma S.r.l. - www.assyoma.it
email: g.danti@assyoma.it - info@assyoma.it
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