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
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