Re: raw vs block speed difference?

[mlelstv%serpens.de@localhost (Michael van Elst)]

agrier%poofygoof.com@localhost ("Aaron J. Grier") writes:

>rsd0a: 1342177280 bytes transferred in 17.588 secs (76312103 bytes/sec)
>sd0a : 1342177280 bytes transferred in 40.806 secs (32891664 bytes/sec)

>why is the raw device > twice the speed of the block device?

The raw device uses IO buffers as you specify and limited to
MAXPHYS (64k).

The block device uses IO buffers the size of a filesystem block
(as recorded in the disk label) or 2048 bytes if DIOCGPART failed.
There is also some overhead for maintaining the buffer cache,
but you CPU is probably fast enough to hide this.

-- 
-- 
                                Michael van Elst
Internet: mlelstv%serpens.de@localhost
                                "A potential Snark may lurk in every tree."