From: Zdenek Kabelac <zkabelac@redhat.com>
To: Gionatan Danti <g.danti@assyoma.it>
Cc: LVM general discussion and development <linux-lvm@redhat.com>
Subject: Re: [linux-lvm] Snapshot behavior on classic LVM vs ThinLVM
Date: Wed, 26 Apr 2017 16:33:15 +0200 [thread overview]
Message-ID: <921a6b9c-103e-3c71-97d2-44ceb5a6bf87@redhat.com> (raw)
In-Reply-To: <c5bee073-7871-fbb9-370d-8a1b322bbd86@assyoma.it>
Dne 26.4.2017 v 15:37 Gionatan Danti napsal(a):
>
> On 26/04/2017 13:23, Zdenek Kabelac wrote:
>>
>> You need to use 'direct' write more - otherwise you are just witnessing
>> issues related with 'page-cache' flushing.
>>
>> Every update of file means update of journal - so you surely can lose
>> some data in-flight - but every good software needs to the flush before
>> doing next transaction - so with correctly working transaction software
>> no data could be lost.
>
> I used "oflag=sync" for this very reason - to avoid async writes, However,
> let's retry with "oflat=direct,sync".
>
> This is the thinpool before filling:
>
> [root@blackhole mnt]# lvs
> LV VG Attr LSize Pool Origin Data% Meta% Move Log
> Cpy%Sync Convert
> thinpool vg_kvm twi-aot--- 1.00g 87.66 12.01
> thinvol vg_kvm Vwi-aot--- 2.00g thinpool 43.83
> root vg_system -wi-ao---- 50.00g
> swap vg_system -wi-ao---- 7.62g
>
> [root@blackhole storage]# mount | grep thinvol
> /dev/mapper/vg_kvm-thinvol on /mnt/storage type ext4
> (rw,relatime,seclabel,errors=remount-ro,stripe=32,data=ordered)
>
>
> Fill the thin volume (note that errors are raised immediately due to
> --errorwhenfull=y):
>
> [root@blackhole mnt]# dd if=/dev/zero of=/mnt/storage/test.2 bs=1M count=300
> oflag=direct,sync
> dd: error writing ‘/mnt/storage/test.2’: Input/output error
> 127+0 records in
> 126+0 records out
> 132120576 bytes (132 MB) copied, 14.2165 s, 9.3 MB/s
>
> From syslog:
>
> Apr 26 15:26:24 localhost lvm[897]: WARNING: Thin pool vg_kvm-thinpool-tpool
> data is now 96.84% full.
> Apr 26 15:26:27 localhost kernel: device-mapper: thin: 253:4: reached low
> water mark for data device: sending event.
> Apr 26 15:26:27 localhost kernel: device-mapper: thin: 253:4: switching pool
> to out-of-data-space (error IO) mode
> Apr 26 15:26:34 localhost lvm[897]: WARNING: Thin pool vg_kvm-thinpool-tpool
> data is now 100.00% full.
>
> Despite write errors, the filesystem is not in read-only mode:
But you get correct 'write' error - so from application POV - you get failing
transaction update/write - so app knows 'data' were lost and should not
proceed with next transaction - so it's in line with 'no data is lost' and
filesystem is not damaged and is in correct state (mountable).
Zdenek
next prev parent reply other threads:[~2017-04-26 14:33 UTC|newest]
Thread overview: 94+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-06 14:31 [linux-lvm] Snapshot behavior on classic LVM vs ThinLVM Gionatan Danti
2017-04-07 8:19 ` Mark Mielke
2017-04-07 9:12 ` Gionatan Danti
2017-04-07 13:50 ` L A Walsh
2017-04-07 16:33 ` Gionatan Danti
2017-04-13 12:59 ` Stuart Gathman
2017-04-13 13:52 ` Xen
2017-04-13 14:33 ` Zdenek Kabelac
2017-04-13 14:47 ` Xen
2017-04-13 15:29 ` Stuart Gathman
2017-04-13 15:43 ` Xen
2017-04-13 17:26 ` Stuart D. Gathman
2017-04-13 17:32 ` Stuart D. Gathman
2017-04-14 15:17 ` Xen
2017-04-14 7:27 ` Gionatan Danti
2017-04-14 7:23 ` Gionatan Danti
2017-04-14 15:23 ` Xen
2017-04-14 15:53 ` Gionatan Danti
2017-04-14 16:08 ` Stuart Gathman
2017-04-14 17:36 ` Xen
2017-04-14 18:59 ` Gionatan Danti
2017-04-14 19:20 ` Xen
2017-04-15 8:27 ` Xen
2017-04-15 23:35 ` Xen
2017-04-17 12:33 ` Xen
2017-04-15 21:22 ` Xen
2017-04-15 21:49 ` Xen
2017-04-15 21:48 ` Xen
2017-04-18 10:17 ` Zdenek Kabelac
2017-04-18 13:23 ` Gionatan Danti
2017-04-18 14:32 ` Stuart D. Gathman
2017-04-19 7:22 ` Xen
2017-04-07 22:24 ` Mark Mielke
2017-04-08 11:56 ` Gionatan Danti
2017-04-07 18:21 ` Tomas Dalebjörk
2017-04-13 10:20 ` Gionatan Danti
2017-04-13 12:41 ` Xen
2017-04-14 7:20 ` Gionatan Danti
2017-04-14 8:24 ` Zdenek Kabelac
2017-04-14 9:07 ` Gionatan Danti
2017-04-14 9:37 ` Zdenek Kabelac
2017-04-14 9:55 ` Gionatan Danti
2017-04-22 7:14 ` Gionatan Danti
2017-04-22 16:32 ` Xen
2017-04-22 20:58 ` Gionatan Danti
2017-04-22 21:17 ` Zdenek Kabelac
2017-04-23 5:29 ` Xen
2017-04-23 9:26 ` Zdenek Kabelac
2017-04-24 21:02 ` Xen
2017-04-24 21:59 ` Zdenek Kabelac
2017-04-26 7:26 ` Gionatan Danti
2017-04-26 7:42 ` Zdenek Kabelac
2017-04-26 8:10 ` Gionatan Danti
2017-04-26 11:23 ` Zdenek Kabelac
2017-04-26 13:37 ` Gionatan Danti
2017-04-26 14:33 ` Zdenek Kabelac [this message]
2017-04-26 16:37 ` Gionatan Danti
2017-04-26 18:32 ` Stuart Gathman
2017-04-26 19:24 ` Stuart Gathman
2017-05-02 11:00 ` Gionatan Danti
2017-05-12 13:02 ` Gionatan Danti
2017-05-12 13:42 ` Joe Thornber
2017-05-14 20:39 ` Gionatan Danti
2017-05-15 12:50 ` Zdenek Kabelac
2017-05-15 14:48 ` Gionatan Danti
2017-05-15 15:33 ` Zdenek Kabelac
2017-05-16 7:53 ` Gionatan Danti
2017-05-16 10:54 ` Zdenek Kabelac
2017-05-16 13:38 ` Gionatan Danti
2018-02-27 18:39 ` Xen
2018-02-28 9:26 ` Zdenek Kabelac
2018-02-28 19:07 ` Gionatan Danti
2018-02-28 21:43 ` Zdenek Kabelac
2018-03-01 7:14 ` Gionatan Danti
2018-03-01 8:31 ` Zdenek Kabelac
2018-03-01 9:43 ` Gianluca Cecchi
2018-03-01 11:10 ` Zdenek Kabelac
2018-03-01 9:52 ` Gionatan Danti
2018-03-01 11:23 ` Zdenek Kabelac
2018-03-01 12:48 ` Gionatan Danti
2018-03-01 16:00 ` Zdenek Kabelac
2018-03-01 16:26 ` Gionatan Danti
2018-03-03 18:32 ` Xen
2018-03-04 20:34 ` Zdenek Kabelac
2018-03-03 18:17 ` Xen
2018-03-04 20:53 ` Zdenek Kabelac
2018-03-05 9:42 ` Gionatan Danti
2018-03-05 10:18 ` Zdenek Kabelac
2018-03-05 14:27 ` Gionatan Danti
2018-03-03 17:52 ` Xen
2018-03-04 23:27 ` Zdenek Kabelac
2017-04-22 21:22 ` Zdenek Kabelac
2017-04-24 13:49 ` Gionatan Danti
2017-04-24 14:48 ` Zdenek Kabelac
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