Dne 03. 06. 19 v 23:12 Ilia Zykov napsal(a):
Presumably you want a thick volume but inside a thin pool so that you
can used snapshots?
If so have you considered the 'external snapshot' feature?
Yes, in some cases they are quite useful. Still, a fast volume
allocation can be an handy addition.
Hello.
Can I use external snapshot for fast zero allocation?
"thpool" - is lvmthin with lvm zeroing disabled
# lvcreate -n ext2T -V 2TiB --thinpool thpool VG
# lvchange --permission r VG/ext2T
# lvcreate -n zeroed_lve -s VG/ext2T --thinpool VG/thpool
Or it will be the same as zeroing enabled?
Hi
It's not clear what do you want to achieve.
External origin for thin-volume is always a read-only LV.
External origin can be of any type - i.e. even thinLV from another thin-pool
and single origin can be used for number of thin volumes with external origin.
For now you CANNOT 'merge' such thinLV with external origin - so the only way
to get 'writable' origin back is to drop all thins that are using it as
external origin.
Now - how the 'zeroing' plays the role here ?
Zeroing is property of thin-pool that serves thinLV.
Unprovisioned blocks always do return 'zeroes'.
When block is provisioned - unwritten portions needs to be zeroed (depending
on zeroing setting) - the bigger the block the bigger the chance the zeroing
will take more time - lvm2 does not recommend using thin-pool with zeroing and
chunksize bigger then 512KB.
Most modern filesystem keep track of written pieces of a block device
themselves, so zeroing has almost no practical use.
Regards
Zdenek
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