Re: Mac OS vs Fedora disk performance

Le 7 mars 2011 à 06:36, Chris Murphy a écrit :

> [...]
> 
> That's essentially the same result as on Linux with the block level device. (Raw/character devices went away some time ago with Linux 2.6, and /dev/sda is definitely block level.)
> 
> Still, it's mysterious why there is such a big difference between /dev/disk0 and /dev/rdisk0 on XNU...it doesn't seem they should be that different. There must be something else going on.

Hello Chris,

For what it is worth, the implementations of dd on Mac OS X and Linux aren't the same: GNU coreutils for the latter, Berkeley for the former.

But in both cases, they end with similar system calls:

	open("/dev/sda", ...)
	open("/dev/disk0", ...)
	open("/dev/rdisk0", ...)

So, it is at the kernel level that the interpretation of device nodes differ; it could well be that, given the initial philosophy of Linux wrt disks, the semantics of open("/dev/sda", ...) tends to be close to the one of open("/dev/rdisk0", ...).

While trying to somewhat refresh my memories about those matters in Linux, I encountered this one:

	http://www.linuxsa.org.au/pipermail/linuxsa/2002-February/038793.html

HTH,
Axel