From owner-freebsd-hackers  Sun Apr  8 14:16:28 2001
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Subject: Re: Mounting partitions with RO flag
In-Reply-To: <20010408222153.O47272-100000@scribble.fsn.hu> from "Attila Nagy" at "Apr 8, 1 10:24:09 pm"
To: bra@fsn.hu (Attila Nagy)
Date: Mon, 9 Apr 2001 01:16:02 +0400 (MSD)
Cc: freebsd-hackers@FreeBSD.ORG
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Attila Nagy writes:
> > > Would it be possible to solve this under FreeBSD?
> > I am second for it.
> I hope somebody will enlighten my dark mind, because I am really curious
> about this :)
> 
> > I am using some partition "magic" and know dark side of it.
> What the problem is with it besides the ugly hacking and the small number
> of possible partitions?
How much partitions do you want?
adNs[0..30][a..h] 31*8= 248
if it is low enough, just use vn[0..]s[0..30][a..h]
... with some more dark sides, of cause

About dark side:
0garkin~(4)#df
Filesystem           1K-blocks     Used    Avail Capacity  Mounted on
...
/dev/ad0s2h            7993324   461995  6891864     6%    /usr
....
/dev/ad0s3a            7993324   441159  6912700     6%    /jail/pent/usr
....
There is physically the same fs marked as /dev/ad0s2h and /dev/ad0s3a
in this example.
The /usr is rw mounted and /jail/pent/usr is ro mounted.
Do you see a difference?

You can really stuck VM system with ro mount that
is really rw mount in another mount.
Instances of shared fs do not share buffers - which IS
a real point - just allow second mount does not solve
a problem IMHO

The only way of use this method of fs sharing
in production is ro mount of any instance and
do not upgrade without all jails stopped. And
a lot of memory for files buffers :-(


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