/yesh onto a new volume, I cannot see the sub directory
/yesh/data001 which was existing before mounting.
If the sub directory is existing where can I find it?
You can use
mount --bind for seeing old mount you have on same mount point.
Create any directory in your filesystem, ex: /mnt/data001, then
mount --bind /yesh/data001 /mnt/data001
This is tricky case, you cannot see old mount and you cant
umount your old mount. Generally
restart is kind of solution but with out restart if you want to access
/yesh/data001 I believe you can achieve via above command.