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From: Zdenek Kabelac <>
To: LVM general discussion and development <>,
	Ilia Zykov <>
Subject: Re: [linux-lvm] Fast thin volume preallocation?
Date: Wed, 5 Jun 2019 12:31:42 +0200	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

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?


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.



  reply	other threads:[~2019-06-05 10:31 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-31 13:13 [linux-lvm] Fast thin volume preallocation? Gionatan Danti
2019-06-03 13:23 ` Joe Thornber
2019-06-03 19:23   ` Gionatan Danti
2019-06-03 21:12     ` Ilia Zykov
2019-06-05 10:31       ` Zdenek Kabelac [this message]
2019-06-04  5:23     ` Ilia Zykov

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