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Description of problem:
After a pvmove the readahead value of lvm is going to be 0
Version-Release number of selected component (if applicable):
Rhel 7.X all
How reproducible:
Doing a pvmove will reproduce the issue.
Steps to Reproduce:
1> Disable tuned
[root@localhost ~]# systemctl status tuned
● tuned.service - Dynamic System Tuning Daemon
Loaded: loaded (/usr/lib/systemd/system/tuned.service; disabled; vendor preset: enabled)
Active: inactive (dead)
Docs: man:tuned(8)
man:tuned.conf(5)
man:tuned-adm(8)
2> Check the current setting of LV.
[root@localhost ~]# lvs -o +devices testvg
LV VG Attr LSize Pool Origin Data% Meta% Move Log Cpy%Sync Convert Devices
lv1 testvg -wi-a----- 1020.00m /dev/sda1(0)
[root@localhost ~]# dmsetup info -C | grep testvg
testvg-lv1 253 0 L--w 0 1 0 LVM-PnvXfWMsSNlCuBBaPjAMrZj0kDozXiGQ6pzs2hetmQegGWlhrtUvOywDlg9oFCX5
[root@localhost ~]# cat /sys/block/dm-0/queue/read_ahead_kb
128
3> Do a pvmove:
[root@localhost ~]# pvmove /dev/sda1 /dev/sda2
/dev/sda1: Moved: 0.39%
/dev/sda1: Moved: 100.00%
4> Check the read_ahead_kb value
[root@localhost ~]# cat /sys/block/dm-0/queue/read_ahead_kb
0
A workaround for this case is vgchange --refresh.
Actual results:
The read_ahead_kb value is getting changed to 0.
Expected results:
It should not change the read_ahead_kb value to 0.
Additional info:
Comment 4Jonathan Earl Brassow
2019-08-19 19:22:56 UTC
how much could this be affecting performance? (see bug 1740648) Are these two bugs related?
I assume LV also checkes 'default' RA set by kernel during creation - and never sets a smaller value that the one set automatically by kernel.
So in this case I assume any LV created on /dev/sdb will use 128KiB RA (256 sectors).
For testing I'd probably suggest to experiment with higher values - whether those are still preserved.
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.
For information on the advisory, and where to find the updated
files, follow the link below.
If the solution does not work for you, open a new bug report.
https://access.redhat.com/errata/RHBA-2020:1129
Description of problem: After a pvmove the readahead value of lvm is going to be 0 Version-Release number of selected component (if applicable): Rhel 7.X all How reproducible: Doing a pvmove will reproduce the issue. Steps to Reproduce: 1> Disable tuned [root@localhost ~]# systemctl status tuned ● tuned.service - Dynamic System Tuning Daemon Loaded: loaded (/usr/lib/systemd/system/tuned.service; disabled; vendor preset: enabled) Active: inactive (dead) Docs: man:tuned(8) man:tuned.conf(5) man:tuned-adm(8) 2> Check the current setting of LV. [root@localhost ~]# lvs -o +devices testvg LV VG Attr LSize Pool Origin Data% Meta% Move Log Cpy%Sync Convert Devices lv1 testvg -wi-a----- 1020.00m /dev/sda1(0) [root@localhost ~]# dmsetup info -C | grep testvg testvg-lv1 253 0 L--w 0 1 0 LVM-PnvXfWMsSNlCuBBaPjAMrZj0kDozXiGQ6pzs2hetmQegGWlhrtUvOywDlg9oFCX5 [root@localhost ~]# cat /sys/block/dm-0/queue/read_ahead_kb 128 3> Do a pvmove: [root@localhost ~]# pvmove /dev/sda1 /dev/sda2 /dev/sda1: Moved: 0.39% /dev/sda1: Moved: 100.00% 4> Check the read_ahead_kb value [root@localhost ~]# cat /sys/block/dm-0/queue/read_ahead_kb 0 A workaround for this case is vgchange --refresh. Actual results: The read_ahead_kb value is getting changed to 0. Expected results: It should not change the read_ahead_kb value to 0. Additional info: