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  • Cache-A: file sizes different on LTO and VTAPE

  • Gerald Goldman

    February 12, 2013 at 7:06 pm

    I archived some files today from our network to our Cache-A. I always copy the files first, then have the LTO sync in order to avoid some problems we have had in the past with our network. The files are the same size on the SAN and the VTAPE, but when they copied to the LTO, they are listed with smaller file sizes.

    I have never noticed this before. In fact, we generally check the tape information in the Cache-A browser interface to make sure all the files from the VTAPE have made it to LTO. The space used has always matched in the past.

    When the tape is filled, I will restore some files to check that they are not corrupted, but in the meantime, what am I missing here? Is something wrong, or does this happen sometimes?

    Long ago I remember that different volumes could show the same file at different sizes, but I thought those problems were sorted out.

    Thanks for any help with this.

    Gerald Goldman
    Director of Post Production
    Grace Creek Media

  • Tom Goldberg

    February 14, 2013 at 4:57 am

    Hi Gerald,

    The question I would ask is, where are you looking at those file sizes? You’re probably checking the source in Finder and using the Mac’s reporting and then comparing them to what the Cache-A reports in the File Manager. Unfortunately, as we’ve had posted on our FAQ page for years, that won’t work:

    My archive session shows a different total number of bytes than my computer – is something wrong?

    As long as your Transfer Summary shows no errors, everything should be fine. Any difference in reported sizes is caused by variations in the way different file systems and operating systems keep track of file sizes.

    In the Mac environment, things changed in this regard substantially with the advent of OS 10.6 – according to MacWorld:

    “There are, believe it or not, now two sets of entirely different terms for these two ways of thinking. For example, a gigabyte, or GB, is now defined as 1,000 bytes cubed, or 1,000,000,000 bytes. A gibibyte, or GiB, is equal to 1024 bytes cubed, or 1,073,741,824 bytes. (The same rules apply for megabyte and mebibyte, which are defined as 1000 bytes squared and 1,024 bytes squared, respectively.)

    Wake up, you in back! Because here’s where Snow Leopard comes in. In previous versions of Mac OS X, Apple used the1024^3 definition of GB. Rather than keep that math and start calling it GiB, Apple has started using the 1000^3 definition.” [click here for more details]

    Even without this change in how sizes are calculated (i.e. a Mac running Tiger or a PC), there are still variations in how file sizes are calculated and you will most likely never see exactly the same number of bytes in both places.

    If your files all transferred without errors, you should be able to ignore these reporting differences.

    Tom Goldberg
    Cache-A Corporation
    602 Park Point Drive
    Golden, CO 80401

  • Gerald Goldman

    February 14, 2013 at 1:50 pm

    Ah. You are right. Previously I was comparing CatDV to LTO, which seem to use the same file size method. I was also checking SAN to VTAPE which both use the same method.

    This time around I was comparing Finder to LTO which is different and in this particular case very different.

    Thanks for the help!

    Gerald Goldman
    Director of Post Production
    Grace Creek Media

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