reminiscence – Why is writing to a ramdisk no sooner than my SSD?


I created a 30GB HFS+ formatted Ramdisk and checked the pace of copying a big file to it utilizing pv. What shocked me was that the pace was about the identical as an area copy on the identical disk (truly, barely decrease, even!):

Native copy

✦ ❯ pv ~/2017.user-dir.tgz > ~/tmp.dat
^C.4GiB 0:00:22 [2.67GiB/s] [===============================================>                               ] 61% ETA 0:00:13

Ramdisk copy

✦ ❯ pv ~/2017.user-dir.tgz > /Volumes/RamDisk/take a look at.dat
27.6GiB 0:00:12 [2.23GiB/s] [=====================>   

I would have assumed that writing to the ramdisk would be on par with the read speed of the SSD (with some overhead due to the file system), but nowhere near this! Any good explanation?