RAMdisk reads seem to be no faster than hard disk (HDD) reads

Question

I created a RAM disk and write speed seems to be 3x as fast, but read speeds are no better than my hard disk. I didn't think this was possible, I thought RAM would always be faster than HDD. Can this be true? Or is my code wrong and garbage in = garbage out?

mkdir /tmp/test
mount -t tmpfs -o size=1g myramdisk /tmp/ramdisk

#RAM DISK WRITE SPEED
dd if=/dev/zero of=/tmp/ramdisk/zero bs=4k count=100000

#HDD WRITE SPEED
dd if=/dev/zero of=/tmp/test/zero bs=4k count=100000

#RAM DISK READ SPEED
dd if=/tmp/ramdisk/zero of=/dev/null bs=4k count=100000

#HDD DISK READ SPEED
dd if=/tmp/test/zero of=/dev/null bs=4k count=100000

rm /tmp/ramdisk/zero
rm /tmp/test/zero

umount /tmp/ramdisk

rmdir /tmp/ramdisk
rmdir /tmp/test

Returns:

100000+0 records out
409600000 bytes (410 MB, 391 MiB) copied, 0.749689 s, 546 MB/s
100000+0 records in
100000+0 records out
409600000 bytes (410 MB, 391 MiB) copied, 2.32925 s, 176 MB/s
100000+0 records in
100000+0 records out
409600000 bytes (410 MB, 391 MiB) copied, 0.39752 s, 1.0 GB/s
100000+0 records in
100000+0 records out
409600000 bytes (410 MB, 391 MiB) copied, 0.365228 s, 1.1 GB/s

My server is AMD Opteron 3350 HE (4168), 4GB RAM (3.7GB free before I created the RAM disk), HDD is 7200 RPM.

Answer 1

it might be that your hdd access is already cached due to previous reads