Re: Backup question

From: Joachim Schipper (jDOTschipper_at_math.uu.nl)
Date: 06/29/05

  • Next message: Phil: "Re: Backup question"
    Date: 29 Jun 2005 10:18:06 GMT
    
    

    In article <slrndc3r7r.cr.ibuprofin@compton.phx.az.us> you wrote:
    > In the Usenet newsgroup alt.computer.security, in article
    > <d9rkbd$9k7$1@home.itg.ti.com>, News wrote:
    >
    >>Ive got a 120G harddrive with about 40G worth of files for my photography /
    >>graphics files. These are very important to me.
    >
    > "How important are they?" Translation - what is it worth to you? Side
    > question, what are you guarding against? Hardware failure? Software failure?
    > Theft? Fire/Flood/Earthquake? Fumbling fingers?
    >
    >>I use Retrospect to guard against problems, but obviously need a backup
    >>to another drive or archive on CD-ROM.
    >
    > 40 Gigs can't be shoehorned into a CD-ROM. How often do these files change?
    >
    >>I am a student also, so cost per MB is important too.
    >
    > What are you guarding against? At the least, you would want a removable
    > media of sufficient capacity (so that it can be elsewhere when your main
    > computer is crushed by stampeding yaks). Thing is, 120 Gig capacity is
    > huge, and even 40 Gigs is going to be expensive. Tape drives of suitable
    > capacity (DDS/4 mm can do 20 Gigs normal "40 Gigs" compressed - the later
    > unlikely if the data is already in a compressed format) are very expensive,
    > but we've had good luck with Seagates. DLTs are even more expensive, but
    > the media is "comparable" in cost. Avoid Travan drives - reliability.

    I'm going to assume you want reliable offsite storage.

    Tapes are a good solution if you do a *lot* of backups - the cost per GB
    of storage is about as good as you can get .

    If you are willing to buy tape drives from eBay and the like, though,
    prices can be pretty acceptable. Think $ 40 for a SCSI adapter (if you
    do not have it already), $ 70 for a DDS-2 drive (4 GB/tape, '8 GB
    compressed') and something like $5 a tape. Which, according to vendor
    specs, can be reused 100 times [and, if you're willing to take the
    chance, will probably last quite a bit longer]. That's pretty close to $
    0.01 a GB, excluding initial costs, guaranteed to retain data for 10
    years. [If you're willing to shell out more for a tape drive, this cost
    will be even lower, as tapes are pretty much the same cost regardless of
    capacity, up to DLT at least.]

    The initial cost is worth considering, but not too high to be feasible.
    The *other* thing worth considering that backups to tape are most useful
    if you can read the tape somewhere after your main computer has been
    thoroughly destroyed by, for example, stampeding yaks. You should also
    consider getting some tapes with better capacity, as the above solution
    would require about 10 tapes. (Universities may have this capacity; ask
    your local operator. If you're really lucky, they might also be dumping
    tape drives...)

    Burning to CD is easy, but not a good long-term solution - it's
    inconvenient, as it'll take about 15 CD's to do a full backup, and CD-Rs
    are hideously expensive (close to $ 1 a GB, if you're willing to store
    them on a spindle and use no-name media). They are also not likely to
    be readable after ten years, especially if mistreated (as they are wont
    to be, if you're anything like me).
    CD-RW's are less expensive, a couple of $$$ per (re-usable) disk, but
    are not exactly reliable, especially when re-used often. This makes them
    less suitable for backups. [I dislike them, partly for no good reason,
    so do not take this at face value. A lot of people happily back up to
    CD-RW, and presumably those backups remain restorable...]
    CD-writers can be had for about $ 50, and the drive will read CD and DVD
    media at that price.

    Burning to DVD is more convenient, but DVD writers are expensive. The
    initial cost is in the 'tape' ballpark, and the cost in the 'CD-R'
    ballpark. That being said, this isn't too inconvenient and DVD's are
    likely to be readable everywhere.

    External hard drives are another option, but aren't exactly 'removable
    media' - the main effect of which is that, though you *could* place them
    offsite, you likely won't. The cost is a few $$$ a GB; they are
    pretty much infinitely reusable. Reading them should be possible on
    newer machines, after some fiddling.

    The last option, of course, is to get the cheapest computer you can
    find, put a decent 40 or 80 GB drive in it, and synchronize data
    nightly. Place it somewhere it'll not be bothered too much, and be sure
    to use encryption while sending your stuff over the net. You should be
    able to get the computer for free by asking around, so this will just
    cost you a single drive and some time. Be sure to place it with a friend
    or somesuch. You might want to look into rsync, or some rsync-derivative
    that will keep old data around for a while. This is cheap, but data will
    only be kept for a couple of weeks and it'll take you a while to
    assemble a stack of CD's or tapes as large as a computer. Or noisy...

    I have, personally, used CD's for a couple of backups, as that's what
    was available, but cringed at the cost and made far too little backups.
    I own an ancient 1/2 GB /tape tape drive, which I plan to use for
    incrementals (and possibly the full backup as well) as soon as the
    system it's attached to becomes stable (currently being installed). If
    this works out, I intend to purchase a slightly more modern tape drive.
    My personal backups take about 12 GB (after compression) for a full
    backup, and are likely to be 15-20 GB for a full backup plus a month's
    incrementals. A DDS-2 or DDS-3 drive seems reasonable.

    My students' association, for which I manage the computers, has close to
    the same storage requirements, but those are expected to grow. It was
    decided to use DVDs here, as backups should be readable without special
    knowledge or hardware. There are plans to mirror data accross redundant
    servers, which would also take care of part of the backup problem
    (notably, head crashes, which are not unlikely given the quality of
    hardware I'm forced to work with - in fact, we've had one hard drive
    stop functioning already. After it had cooled down, we were able to
    restore the data on the disk in apparently good condition; the system
    portion was restored from backups).

    In both cases, nightly backups are written to an internal disk. Those
    are not intended to guard against disaster, but are quite useful in case
    of an operator error. Yes, I've used them (after 'chown -R root:root /',
    'rm -rf /var/someimportantdir', editing configuration files into
    un-usability, or removing important personal data).

    In all cases, get some decent backup software that will let you do
    incremental backups.

                    Joachim


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