The issue is that mount_mfs is simply newfs with a catch: it
constructs the new filesystem completely in memory and lives on as
the storage for the mounted filesystem. If you view the processes on
a system using MFS, you will notice that one of them is the original
mount_mfs, having become a daemon.
Yes, things are stored twice in memory: once in the buffer cache and
once in the MFS process. Yes, they are also copied multiple times.
MFS simply can't perform as well as you might expect. The malloc disk
device can because it simply creates a kernel-memory backing store.
The disadvantage here is that it's wired memory and can't get swapped
out like mount_mfs can.
--
Brian Fundakowski Feldman \ FreeBSD: The Power to Serve! /
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