[dm-devel] how to refresh LV to apply fstrim online

[Gianluca Cecchi]

Hello,
I have a cluster in RH EL 6.5 (I also have a case open fwiw...) where I'm
using HA-LVM.
I made an upgrade of the storage array Netappp -> Netapp.
I was able to do it online without service disruption using pvmove.
As a side effect the destination storage array reports the target LUN as
100% used due to the pvmove operation itself and how it works.
The LUN is now thin provisioned but it was not when pvmove was executed,
and running fstrim on the fs gives error

[root at dbatest1 ~]# fstrim /ALM/rdoffline
fstrim: /ALM/rdoffline: FITRIM ioctl failed: Operation not supported
[root at dbatest1 ~]#

The fs is on an LV with its PV on a multipath device

[root at dbatest1 ~]# df -h /ALM/rdoffline
Filesystem            Size  Used Avail Use% Mounted on
/dev/mapper/VG_ALMTEST_RDOF-LV_ALMTEST_RDOF
                       50G  1.9G   45G   4% /ALM/rdoffline

[root at dbatest1 ~]# pvs|grep VG_ALMTEST_RDOF
  /dev/mapper/3600a098038303769752b495147377858 VG_ALMTEST_RDOF lvm2 a--
 50.00g    0
[root at dbatest1 ~]#

[root at dbatest1 ~]# multipath -l
/dev/mapper/3600a098038303769752b495147377858
3600a098038303769752b495147377858 dm-40 NETAPP,LUN C-Mode
size=50G features='4 queue_if_no_path pg_init_retries 50
retain_attached_hw_handle' hwhandler='1 alua' wp=rw
`-+- policy='round-robin 0' prio=0 status=active
  |- 7:0:5:14 sddt 71:176  active undef running
  `- 8:0:5:14 sdef 128:112 active undef running
[root at dbatest1 ~]#

At storage array level the LUN appears as 100% used even if it is almost
empty
I found a way to do the fstrim and reclaim space at storage array level,
but only giving downtime, with this sequence of steps:

1) rescan single paths of the multipath device
[root at dbatest1 ~]# for dev in sddt sdef; do echo "1" >
/sys/block/${dev}/device/rescan; done

2) restart multipathd daemon
[root at dbatest1 ~]# service multipathd restart
ok
Stopping multipathd daemon:                                [  OK  ]
Starting multipathd daemon:                                [  OK  ]
[root at dbatest1 ~]#

3) disable/enable the cluster service that contains the fs resource where I
operated 1) and 2)
[root at dbatest1 ~]# clusvcadm -d ALMTEST
Local machine disabling service:ALMTEST...Success

[root at dbatest1 ~]# clusvcadm -e ALMTEST
Local machine trying to enable service:ALMTEST...Success
service:ALMTEST is now running on icldbatest1
[root at dbatest1 ~]#

4) now fstrim works ok
 [root at dbatest1 ~]# fstrim /ALM/rdoffline
[root at dbatest1 ~]#
(it takes about 10-20 seconds, depending on the work it has to do..)

It seems each of the 3 steps is necessary. If I don't execute one of them,
I keep getting the error.

Is there a way to refresh the LVM part, without disabling the service, that
corresponds to without deactivating/activating the LV?

I tried the --refresh option but it didn't work.

Thanks in advance,
Gianluca
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