From: Gionatan Danti <g.danti@assyoma.it>
To: Zdenek Kabelac <zkabelac@redhat.com>
Cc: "Dalebjörk, Tomas" <tomas.dalebjork@gmail.com>,
"LVM general discussion and development" <linux-lvm@redhat.com>
Subject: Re: [linux-lvm] exposing snapshot block device
Date: Wed, 23 Oct 2019 19:16:05 +0200 [thread overview]
Message-ID: <65a61709788b69c722572dac76cf02a2@assyoma.it> (raw)
In-Reply-To: <13d450bf-f6ad-7db8-eec1-88c4eb473287@redhat.com>
Il 23-10-2019 17:37 Zdenek Kabelac ha scritto:
> Hi
>
> If you use 1MiB chunksize for thin-pool and you use 'dd' with proper
> bs size
> and you write 'aligned' on 1MiB boundary (be sure you user directIO,
> so you are not a victim of some page cache flushing...) - there should
> not be any useless read.
>
> If you still do see such read - and you can easily reproduce this with
> latest kernel - report a bug please with your reproducer and results.
>
> Regards
>
> Zdenek
OK, I triple-checked my numbers and you are right: on a fully updated
CentOS 7.7 x86-64 box with kernel-3.10.0-1062.4.1 and lvm2-2.02.185-2,
it seems that the behavior I observed on older (>2 years ago) is not
present anymore.
Take this original lvm setup:
[root@localhost ~]# lvs -o +chunk_size
LV VG Attr LSize Pool Origin Data% Meta% Move
Log Cpy%Sync Convert Chunk
root centos -wi-ao---- <6.20g
0
swap centos -wi-ao---- 512.00m
0
thinpool centos twi-aot--- 1.00g 25.00 14.16
64.00k
thinvol centos Vwi-a-t--- 256.00m thinpool 100.00
0
Taking a snapshot (lvcreate -s /dev/centos/thinvol -n thinsnap) and
overwriting 1 MB of data on origin via "dd if=/dev/urandom
of=/dev/centos/thinvol bs=1M count=32 oflag=direct" results in the
following I/O to/from disk:
[root@localhost ~]# dstat -d -D sdc
---dsk/sdc---
read writ
1036k 32M
As you can see, while 1 MB was indeed read (due to metadata read?), no
other read amplification occoured.
Now I got curious to see if zeroing behave in the same manner. So, I
deleted thinsnap & thinvol, toggled zeroing on (lvchange -Zy
centos/thinpool), and recreated thinvol:
[root@localhost ~]# lvs -o +chunk_size
LV VG Attr LSize Pool Origin Data% Meta% Move
Log Cpy%Sync Convert Chunk
root centos -wi-ao---- <6.20g
0
swap centos -wi-ao---- 512.00m
0
thinpool centos twi-aotz-- 1.00g 0.00 11.04
64.00k
thinvol centos Vwi-a-tz-- 256.00m thinpool 0.00
0
[root@localhost ~]# dstat -d -D sdc
--dsk/sdc--
read writ
0 13M
520k 19M
Again, no write amplificaton occoured.
Kudos to all the team for optimizing lvmthin in this manner, it really
is a flexible and great performing tool.
Regards.
--
Danti Gionatan
Supporto Tecnico
Assyoma S.r.l. - www.assyoma.it
email: g.danti@assyoma.it - info@assyoma.it
GPG public key ID: FF5F32A8
prev parent reply other threads:[~2019-10-23 17:16 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-22 10:47 [linux-lvm] exposing snapshot block device Dalebjörk, Tomas
2019-10-22 13:57 ` Zdenek Kabelac
2019-10-22 15:29 ` Dalebjörk, Tomas
2019-10-22 15:36 ` Zdenek Kabelac
2019-10-22 16:13 ` Dalebjörk, Tomas
2019-10-23 10:26 ` Zdenek Kabelac
2019-10-23 10:56 ` Tomas Dalebjörk
2019-10-22 16:15 ` Stuart D. Gathman
2019-10-22 17:02 ` Tomas Dalebjörk
2019-10-22 21:38 ` Gionatan Danti
2019-10-22 22:53 ` Stuart D. Gathman
2019-10-23 6:58 ` Gionatan Danti
2019-10-23 10:06 ` Tomas Dalebjörk
2019-10-23 10:12 ` Zdenek Kabelac
2019-10-23 10:46 ` Zdenek Kabelac
2019-10-23 11:08 ` Gionatan Danti
2019-10-23 11:24 ` Tomas Dalebjörk
2019-10-23 11:26 ` Tomas Dalebjörk
2019-10-24 16:01 ` Zdenek Kabelac
2019-10-25 16:31 ` Tomas Dalebjörk
2019-11-04 5:54 ` Tomas Dalebjörk
2019-11-04 10:07 ` Zdenek Kabelac
2019-11-04 14:40 ` Tomas Dalebjörk
2019-11-04 15:04 ` Zdenek Kabelac
2019-11-04 17:28 ` Tomas Dalebjörk
2019-11-05 16:24 ` Zdenek Kabelac
2019-11-05 16:40 ` Mikulas Patocka
2019-11-05 20:56 ` Tomas Dalebjörk
2019-11-06 9:22 ` Zdenek Kabelac
2019-11-07 16:54 ` Mikulas Patocka
2019-11-07 17:29 ` Tomas Dalebjörk
2020-09-04 12:09 ` Tomas Dalebjörk
2020-09-04 12:37 ` Zdenek Kabelac
2020-09-07 13:09 ` Mikulas Patocka
2020-09-07 14:14 ` Dalebjörk, Tomas
2020-09-07 14:17 ` Zdenek Kabelac
2020-09-07 16:34 ` Tomas Dalebjörk
2020-09-07 16:42 ` Zdenek Kabelac
2020-09-07 17:37 ` Tomas Dalebjörk
2020-09-07 17:50 ` Zdenek Kabelac
2020-09-08 12:32 ` Dalebjörk, Tomas
2020-09-07 19:56 ` Tomas Dalebjörk
2020-09-07 20:22 ` Tomas Dalebjörk
2020-09-07 21:02 ` Tomas Dalebjörk
2019-10-23 12:12 ` Ilia Zykov
2019-10-23 12:20 ` Ilia Zykov
2019-10-23 13:05 ` Zdenek Kabelac
2019-10-23 14:40 ` Gionatan Danti
2019-10-23 15:46 ` Ilia Zykov
2019-10-23 12:59 ` Zdenek Kabelac
2019-10-23 14:37 ` Gionatan Danti
2019-10-23 15:37 ` Zdenek Kabelac
2019-10-23 17:16 ` Gionatan Danti [this message]
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