hi,
i like to know if the below conbfiguration is raid 0.

sudo lvdisplay -m|more
--- Logical volume ---
LV Path /dev/y/test
LV Name test
VG Name y
LV UUID oLKKGm-lIOW-6XmQ-P2Z9-1AiK-WB5t-I8VfXZ
LV Write Access read/write
LV Creation host, time test, 2018-04-14 10:25:42 +0000
LV Status available
# open 1
LV Size 118.99 GiB
Current LE 30462
Segments 3
Allocation inherit
Read ahead sectors auto
- currently set to 8192
Block device 253:5

--- Segments ---
Logical extents 0 to 12798:
Type linear
Physical volume /dev/sdb1
Physical extents 0 to 12798

Logical extents 12799 to 25597:
Type linear
Physical volume /dev/sdb2
Physical extents 0 to 12798

Logical extents 25598 to 30461:
Type linear
Physical volume /dev/sdc1
Physical extents 0 to 4863

RAID 0 is striping. You LV is not striped.

then what is this lv?

A non-striped, non-mirrored logical volume. Also known as a linear logical volume.

linear or concatenated.right?
the data will be written first in /dev/sdb1,when this is full then will write in /dev/sdb2.

The correct term is "linear", but "concatenated" is a correct description.

This is not correct. Let's create a scenario:

sdc is free.
Volume 1 has physical extents on sdb.
Volume 2 also has physical extents on sdb.
Volume 1 is extended - new physical extents come from sdc.
Volume 2 is removed.
Volume 1 is extended again - new physical extents may come from sdb.

"linear" means that there is no mirroring, striping or other RAID level. You can also ask for a volume to be contiguous; in this case, I think it will be allocated as you say.

then how data is written on lv?

Just like any other storage device.

Remember that storage is random-access. You can write blocks sequentially, or you can seek to a position and write at that position. Therefore, data is not written from the beginning to the end, as you said.

When dealing with linear logical volumes, each logical extent is mapped to exactly one physical extent. When you write to the logical volume sequentially, you start at the first logical extent, filling the corresponding physical extent. When the extent is full, you continue at the second logical extent, filling the corresponding physical extent. And so on.