Backups: rsync, software RAID, other strategies?

From: Bob Johnson (bob89_at_bobj.org)
Date: 03/07/04

  • Next message: Gary W. Swearingen: "Re: SIngle User Mode Help" 
    To: questions@freebsd.org
Date: Sun, 7 Mar 2004 01:52:55 -0500

    A bunch of related questions:

    I'm setting up a small mail and file server. The mail server part will
    be Courier, while the file server part will primarily be used via NFS
    and Samba to store backups of my desktop and laptop computers.

    The system has a pair of WD1600JB 160 GB ATA 100 drives in it, both on a
    single Promise PDC20268 UDMA100 controller, but each on a separate
    channel (i.e. both are masters with no slaves). My plan is to use one
    of the drives as a backup for the other. I want to use a backup method
    that creates a mirror of the working drive so that if it fails, I can
    simply mount the backup in place of the working drive, and get back in
    business. The operating system will (probably) not be on either of
    these drives, they will only host /home where mail and backup files
    will reside.

    I've tentatively decided to synchronize the mirror to the working drive
    with rsync run once a night (perhaps more often later). This risks
    losing up to a day of mail, but that's probably not the end of the
    world. The reasoning I used was that if I use software RAID, an
    unexpected power failure during a large write operation (yes, it will
    be on a UPS) could corrupt both drives. Running rsync once a night
    would reduce the risk of a failure that damaged both drives, since
    their write activity would not be so strongly correlated.

    Is my fear of losing both drives in a software RAID (mirrored drives)
    configuration a reasonable one? Or is that not going to happen?

    If I use rsync with -delete to maintain a mirror of the primary drive,
    what happens when the primary drive fails? Is there a scenario that
    causes rsync to duplicate all the missing data on the primary drive by
    deleting it from the mirror drive (I've heard of this happening to
    someone, but I believe he was using a homegrown perl script rather than
    rsync).

    Is Courier compatible with this scheme? Or does it care about inode
    numbers or some such thing that will make the backup copy useless?

    Is there any chance it would make sense to use the Coda file system for
    this?

    Do any of the answers change if the mail server ends up on a remote
    system, but I still want the maildirs backed up on the file server?

    Any other suggestions that don't involve buying new hardware? An IDE
    RAID controller would be nice, but buying one isn't on my list of
    things to do. But if I DID break down and buy a new controller card,
    what should it be?

    Thanks,

    - Bob
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  • Next message: Gary W. Swearingen: "Re: SIngle User Mode Help"

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