vgextend error

Hi,
I try to add disk to exciting LVM:

1) I created pv dnd it was successful

[root@sftp idurfoto]# pvscan
PV /dev/vda2 VG centos lvm2 [47.51 GiB / 44.00 MiB free]
PV /dev/vdb VG sftpvg lvm2 [1.98 TiB / 0 free]
PV /dev/vdc VG sftpvg lvm2 [1.98 TiB / 0 free]
PV /dev/vdd VG sftpvg lvm2 [1.98 TiB / 0 free]
PV /dev/vde VG sftpvg lvm2 [1024.00 GiB / 0 free]
PV /dev/vdf lvm2 [300.00 GiB]
Total: 6 [7.29 TiB] / in use: 5 [7.00 TiB] / in no VG: 1 [300.00 GiB]
[root@sftp idurfoto]#

2) try to extend VG but getting error:

[root@sftp idurfoto]# vgextend sftpvg /dev/mapper/sftpvg-sftp
Can't open /dev/sftpvg/sftp exclusively. Mounted filesystem?

[root@sftp idurfoto]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/centos-root 46G 6.0G 40G 14% /
devtmpfs 909M 0 909M 0% /dev
tmpfs 920M 0 920M 0% /dev/shm
tmpfs 920M 8.5M 912M 1% /run
tmpfs 920M 0 920M 0% /sys/fs/cgroup
/dev/vda1 497M 172M 326M 35% /boot
/dev/mapper/sftpvg-sftp 7.0T 7.0T 3.2M 100% /sftp
tmpfs 184M 0 184M 0% /run/user/0
tmpfs 184M 0 184M 0% /run/user/1107
tmpfs 184M 0 184M 0% /run/user/1002
[root@sftp idurfoto]#

is't because thr /sftp is full?

Kind Regards
Mehrdad