extremely large vcf file generated using sam tools

[janaahan13]

Hi,

This is my first time to Samtools. I tried to create .vcf files for my bam files of my paired-end RNA seq samples. I used

samtools mpileup -D -B -Q 20 -u -f /WholeGenomeFasta/genome.fa Sample.bam | bcftools view -gc - > Sample_positions.vcf

But for ~4GB of bam file it is creating(still running) ~ 75GB size of vcf file.

Is this normal or am I making a mistake some where?

Thanks in advance.