More into /etc/rc.d/jail

Glenn Dawson glenn at antimatter.net
Wed Aug 10 05:54:56 GMT 2005


At 02:43 PM 8/9/2005, Jeremie Le Hen wrote:

>This was recently discussed in some thread.  The problem with this
>approach is that file backed md(4) devices are too slow to make it
>standard.  This is why this won't go into FreeBSD, IMHO.

I experienced the same performance problem when comparing md(4) virtual 
disks in 5.x to vn(4) virtual disks in 4.x.

The results were that md(4) file backed disks in 5.x was only about 1/3 the 
speed of vn(4) file backed disks in 4.x.

Ultimately it turned out that newfs in 5.x creates ufs1 file systems which 
are quite different than the same file system created with newfs in 
4.x.  The most notable difference was that in 5.x each cylinder group 
essentially only had one cylinder in it.

When a file system was created in 4.x and then mounted in 5.x using md(4), 
the performance was almost identical to the performance of vn(4) in 4.x.

I posted a message about it on the freebsd-fs list, but never received any 
feedback.

-Glenn



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