From: Zdenek Kabelac <zkabelac@redhat.com>
To: LVM general discussion and development <linux-lvm@redhat.com>,
Ilia Zykov <mail@service4.ru>
Subject: Re: [linux-lvm] Fast thin volume preallocation?
Date: Wed, 5 Jun 2019 12:31:42 +0200 [thread overview]
Message-ID: <62bf5632-0cca-6bc8-191e-b931e12db827@redhat.com> (raw)
In-Reply-To: <d831c385-b935-0c95-c900-f724468cec1f@service4.ru>
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
next prev parent 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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