Hi Sandeep
Can you perhaps try this for your preseed?
d-i partman-auto/disk string /dev/sda
d-i partman-auto/choose_recipe select root_swap
d-i partman-auto/method string lvm
d-i partman-auto/purge_lvm_from_device boolean true
d-i partman-auto-lvm/guided_size string 100%
d-i partman-auto-lvm/no_boot boolean true
d-i partman/choose_partition select finish
d-i partman/confirm boolean true
d-i partman/confirm_nooverwrite boolean trued-i partman-lvm/device_remove_lvm boolean trued-i partman-partitioning/confirm_write_new_label boolean true
d-i partman-lvm/device_remove_lvm_span boolean truevg_name{ i3vg } \ .
d-i partman-auto/expert_recipe string i3 :: \
153600 100 153600 ext4 \
$defaultignore{ } \
$primary{ } \
method{ lvm } \
device{ /dev/sda } \mountpoint{ / } . \
120000 10 120000 ext4 \
$defaultignore{ }
$lvmok{ } lv_name{ root } \
method{ format } format{ } \
use_filesystem{ } filesystem{ ext4 } \method{ swap } format{ } .
25000 20 25000 linux-swap \
$lvmok{ } lv_name{ swap_1 } \
Good luck
Iain