My RNA-Seq data is in format of fastq(ungzipped from fastq.gz format).I used STAR 2.5.3a mapping the reads with already indexed reference genome. It seems good. But I found the size of generated SAM file is strange. My original input fastq data is like 1.3-1.5 GB, but the SAM file ranges from 3.8 GB to 4.5 GB. Is that normal? If not, what is something wrong there?