Re: md device backing files on nfs mounts?

From: Lowell Gilbert (freebsd-questions-local_at_be-well.ilk.org)
Date: 10/06/05

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    To: "Chad Leigh -- Shire.Net LLC" <chad@shire.net>
Date: 06 Oct 2005 13:18:47 -0400

    "Chad Leigh -- Shire.Net LLC" <chad@shire.net> writes:

    > On Oct 6, 2005, at 10:51 AM, Lowell Gilbert wrote:
    >
    > > "Chad Leigh -- Shire.Net LLC" <chad@shire.net> writes:
    > >
    > >
    > >> Can the files that back an md device be resident on an nfs mount?
    > >>
    > >> I run some jails with each having its own root based on an md
    > >> device.
    > >> I am thinking of having a backend nfs server have all the storage
    > >> and
    > >> serve it to various front end servers. If one front end server went
    > >> down I could easily bring it up on another one. Kind of poor-man's
    > >> redundancy
    > >>
    > >
    > > How do you get the NFS mount before you have a root?
    >
    > Just the jails would be on md devices on the nfs mounted filesystem.
    > Ie, main computer boots normally, mounts nfs filesystem, then mounts
    > md devices backed by files on the nfs fielsystem

    Yes, okay, that seems obvious now. Maybe I need more caffeine.

    I just tried it without the jails and was able to mount and use the
    filesystem. The permissions *are* a little tricky, because root is
    (as usual) mapped to nobody on my NFS mounts, and needs write access
    on the backing file.

    I did the procedure from the last example in the mdconfig(8) manual,
    and it worked just like on a local disk. There might have been some
    anomalies with the output of ls(1), but I can't reproduce those now.

    You might want to try measuring performance if you implement this; it
    could have some strange interactions with VM and buffering.

    Clever idea, by the way.

    >
    > Chad
    >
    > > Also, I suspect the permissions might be a little tricky...
    > >
    > > Some kind of netbooting might work. 

    -- 
Lowell Gilbert, embedded/networking software engineer, Boston area
		http://be-well.ilk.org/~lowell/
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