Doctor said i should get a biopsy on my 6.5mm thyroid nodule. it's hypoechoic and nothing else suspicious on ultrasound. he said it's for "peace of mind". is this normal practice for a small nodule?

No: There are guidelines set out on what to biopsy. Google: sru thyroid consensus and there is a chart. If you are the type who will lose sleep over it being cancer or not then you could biopsy for your peace of mind but if it were me, i would not want a biopsy.

Thyroid nodule: This is something that i would likely recommend repeat ultrasound in 6 months and possible suppression treatment rather then fna. However, always discuss your concerns we your treating doctor.

Watch or biopsy : Small thyroid nodules can be biopsied or followed to see if they grow. Some practitioners will wait until the nodule is 10mm before attempting a biopsy.