NetBSD block vs raw disk I/O

[Sad Clouds <cryintothebluesky%gmail.com@localhost>]

Hello, I have LSI RAID card with 2 RADI0 SSD drives

sd0 at scsibus0 target 0 lun 0: <LSI, MR9260-8i, 2.13> disk fixed
sd0: fabricating a geometry
sd0: 952 GB, 975744 cyl, 64 head, 32 sec, 512 bytes/sect x 1998323712
sectors

Reading from the virtual RAID drive gives throughput of 892MB/sec for
raw device, but only 53MB/sec for block device. This is NetBSD-8

localhost# dd if=/dev/rsd0d of=/dev/null bs=1m count=10000
10000+0 records in
10000+0 records out
10485760000 bytes transferred in 11.749 secs (892481062 bytes/sec)

localhost# dd if=/dev/sd0d of=/dev/null bs=1m count=10000
10000+0 records in
10000+0 records out
10485760000 bytes transferred in 196.552 secs (53348528 bytes/sec)

Any ideas why block device I/O is so abysmal? Is this something
specific to NetBSD?