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:
[root@blackhole mnt]# touch /mnt/storage/test.txt; sync; ls -al
/mnt/storage
total 948248
drwxr-xr-x. 3 root root 4096 26 apr 15.27 .
drwxr-xr-x. 6 root root 51 20 apr 15.23 ..
drwx------. 2 root root 16384 26 apr 15.24 lost+found
-rw-r--r--. 1 root root 838860800 26 apr 15.25 test.1
-rw-r--r--. 1 root root 132120576 26 apr 15.26 test.2
-rw-r--r--. 1 root root 0 26 apr 15.27 test.txt
I can even recover free space via fstrim:
[root@blackhole mnt]# rm /mnt/storage/test.1; sync
rm: remove regular file ‘/mnt/storage/test.1’? y
[root@blackhole mnt]# fstrim -v /mnt/storage/
/mnt/storage/: 828 MiB (868204544 bytes) trimmed
[root@blackhole mnt]# lvs
LV VG Attr LSize Pool Origin Data% Meta%
Move Log Cpy%Sync Convert
thinpool vg_kvm twi-aot--- 1.00g 21.83 3.71
thinvol vg_kvm Vwi-aot--- 2.00g thinpool 10.92
root vg_system -wi-ao---- 50.00g
swap vg_system -wi-ao---- 7.62g
From syslog:
Apr 26 15:34:15 localhost kernel: device-mapper: thin: 253:4: switching
pool to write mode
To me, it seems that metadata updates completed because they hit the
already-allocated disk space, not triggering the remount-ro code. I am
missing something?
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
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