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Date:      Mon, 05 Apr 1999 07:10:36 -0700
From:      Cy Schubert - ITSD Open Systems Group <Cy.Schubert@uumail.gov.bc.ca>
To:        Michael Haro <mharo@area51.fremont.ca.us>
Cc:        stable@FreeBSD.ORG
Subject:   Re: How safe is NULLFS? 
Message-ID:  <199904051410.HAA55376@cwsys.cwsent.com>
In-Reply-To: Your message of "Sun, 04 Apr 1999 23:54:35 PDT." <19990404235435.A37110@patrol.area51.fremont.ca.us> 

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In message <19990404235435.A37110@patrol.area51.fremont.ca.us>, Michael 
Haro wr
ites:
> Hi, I'd like to use NULLFS for a project I'm doing.  The manpage for
> mount_null has...
> BUGS
>    THIS FILESYSTEM TYPE IS NOT YET FULLY SUPPORTED (READ: IT DOESN'T WORK)
>    AND USING IT MAY, IN FACT, DESTROY DATA ON YOUR SYSTEM.  USE AT YOUR OWN
>    RISK.  BEWARE OF DOG.  SLIPPERY WHEN WET.
> 
> I was wondering how dangerous this really is.  If I'm using it to mount
> part of my filesystem as read-only is there still a chance of harm to my 
> system?   Should I just get another hard drive and majorly partition it
> so I can get all the mounts where I want them and mount that drive
> read-only everywhere needed?   Basicly I'm trying to create a chrooted
> copy of the base freebsd install which can be modified but while still
> having the original copy.  I guess what I want to do is mix NULLFS and 
> UNION together.

I've been using nullfs and unionfs since 2.2.2.  There are bugs in 
nullfs and unionfs, one of which supplys a zero to vfs that causes a 
divide by zero exception and panic.  Take a look at PRs 5355, 5212, 
5152, and 4491.  IME, I haven't lost any data due to the use of nullfs 
and unionfs.


Regards,                       Phone:  (250)387-8437
Cy Schubert                      Fax:  (250)387-5766
Open Systems Group          Internet:  Cy.Schubert@uumail.gov.bc.ca
ITSD                                   Cy.Schubert@gems8.gov.bc.ca
Province of BC
                      "e**(i*pi)+1=0"





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