mfs and vnconfig questions out of curiosity
andy at strugglers.net
Sat Apr 17 06:30:55 PDT 2004
I haven't yet had any cause to use memory filesystems in FreeBSD,
but I was just reading about them the other day and I came across
references to malloc-backed and swap-backed.
I have read the man page for vnconfig and mfs on -STABLE, and for
mdconfig on -CURRENT, but I'm still a little confused and would
appreciate some clarifications. So I have a few questions which I
will try to keep relevant to -STABLE, although if the situation has
significantly changed in -CURRENT then a commnent about that would
be appreciated too..
So you can make a swap-backed filesystem in -STABLE with vnconfig
-S, but why would you ever want to do this? Why is this preferred
over just using a regular file?
Then there is malloc-backed filesystem as created with mfs in
STABLE. Presumably this works with virtual memory and lazy
allocation the same way as malloc() from a program would do, i.e.
it is possible to create an FS that is bigger than the amount of
physical memory in the system, and whenever files are stored in the
FS it is similar to any other request to the VM system, may be
satisfied with real memory or go into swap?
I understand that in -CURRENT, mdconfig replaces vnconfig for
managing MFS that are either malloc-backed, swap-backed or
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