Re: better disk reliability on a desktop machine

From: Alex Zbyslaw (xfb52_at_dial.pipex.com)
Date: 07/15/05

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    Date: Fri, 15 Jul 2005 18:57:13 +0100
To: freebsd-questions@freebsd.org

    Chuck Swiger wrote:

    > Nick Barnes wrote:
    > [ ... ]
    >
    >> 3c: Opinions on using firewire hard disks for this at all? Would I be
    >> better off writing DVDs?
    >
    >
    > Hard drives provide near-online backup, but only a single full
    > iteration. You can do incrementals to DVD or CD-RW or tape, and keep
    > many iterations handy, which is far more reliable.

    A recent message on this list was from someone detailing the lengths
    they went to to prevent DVD backups from becoming unusable. A search on
    DVD ought to find it. Mind you, I have heard people say that DAT is
    unreliable whereas (fingers crossed) it has proved fine for me.

    >
    >> 3. making backups.
    >>
    >> 3a: I'm used to dump/restore, but it seems to me that rsync might be a
    >> better tool for this, as it would allow me to mount and browse the
    >> backup. Opinions?
    >
    >
    > This is good if you set up an entire system as a backup, although you
    > could dual-purpose that box and have it act as a fileserver, proxy
    > server, who knows, as well.

    I was planning something along these lines as well. My intention is to
    have an oldish box that I can rsync to at regular intervals (probably
    from filesystem snapshots) in such a way that this would a) provide data
    backup b) provide machine backup as well. In the meantime, it can be a
    web server or a gateway or whatever.

    Originally I was going to run a couple disks with hardware RAID 1, since
    the motherboard has twin SATA RAID controllers. But I think I'm
    changing my mind.

    I've always been a bit dubious of the advantage of RAID 1. Starting
    with two identical disks which came off the assembly line possibly
    within minutes of each other, then assuming that one fails, I believe
    that the odds of the second one also failing are greatly increased. And
    ghods forbid, the disks you get turn out to be the next Deskstar 60 (or
    was it 75?). Then there is the chance of controller failure. And then
    there's the knowing if one of your RAID 1 disks has actually failed.
    Unless there is a CLI for your RAID, or FreeBSD knows enough about it,
    one disk could fail and you might not even know it, especially if you
    don't reboot regularly, or don't watch the machine POST. On most
    desktop machines, you're stuck with one disk activity LED, which is no
    help. Even one LED per controller isn't good enough.

    So my new plan is to have two disks running RAID 0 and to rsync them
    regularly to a different kind of disk which isn't raided at all and
    which is on a different controller, as well as to the remote machine.
    If one of the raided disks fails, then I lose some amount of work,
    depending on how often an rsync is practical. I'm prepared to live with
    that risk given that I think RAID 0 will give great benefits in some of
    the long-winded, disk-intensive, database-y stuff I do. No doubt
    someone can tell me the error of my plan :-) So far, it is all theory.

    This is in addition to tape.

    David Kelly wrote:

    > There are a few select files on the root filesystem which are unique
    > to your system, everything else exists elsewhere such as on your
    > installation CDROM.
    >
    > When you go to build your new filesystem keep a list of the files you
    > tweak. Suggest placing it in /root/important_file_list. Be sure to
    > list the important file list in your important file list.
    >
    > tar -cvzf /home/myaccount/backups/today.tar.gz -T /root/
    > important_file_list
    >
    > Size /usr sufficient for OS and application space but don't place
    > critical data there. Make /home your redundant mirror and put
    > everything critical there.

    Can't argue with the principle. Don't forget that there are system
    specific files on /usr/local as well. Most of it comes straight out of
    ports but there there are the config files, tweaked startup files,
    scripts in /usr/local/bin etc. Also, if you don't have a list of the
    ports you have, then /var/db becomes important as well.

    --Alex

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