Ssd slow speed on goflex home running Debian-4.12.1-kirkwood (no replies)

I have goflex home running Debian-4.12.1-kirkwood-tld-1-rootfs-bodhi.tar.bz2 on Colorful SL300 128GB via SATA port

I just tried a dd test and speed only 47MB/s it's too slow for SSD hard disk device

Quote

root@debian:~# dd if=/dev/zero of=/output.img bs=1024k count=1k
1024+0 records in
1024+0 records out
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 22.5388 s, 47.6 MB/s
root@debian:~#

Anyone got this issue, is that hardware limit or something from kernel/os/u-boot
Is there any way to improve the speed?
Thanks,