Basic RAID questions (not buying advice).

Discussion in 'Mac Basics and Help' started by Evolvere, Apr 8, 2010.

  1. Evolvere macrumors member

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    York, UK
    #1
    After doing some research today I still have a few basic questions about RAID arrays that I was hoping someone could answer.

    1) Could I form a RAID 1 set using only two external HDDs, of the exact same capacity, make and model, and a MacBook with OS 10.5? That is, would I only need to connect the laptop to the external HDD enclosures, and the enclosures to each other, with the relevant cables and the software would do the rest?

    2) I kept coming across the warning that a RAID array is redundancy and NOT a backup system. This seems simple enough: a file deleted accidentally on the source drive is deleted on the RAID array. So would I be right in saying that a RAID array along with a system running, say Carbon Copy Cloner with its archival backup, would provide both backup and redundancy?

    Thanks
     
  2. Evolvere thread starter macrumors member

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    #2
    After doing some more reading, I think my initial assumptions to both questions was right, although I understand that true backup means off-site backup too. But could someone please explain to me what my best option would be in terms of setting up the two external HDDs?

    For arguments sake, say I have two OWC Mercury Elite 1TB drives connected too each other and to my MacBook via friewire, and I run Carbon Copy Cloner with archival backup. I want one of the external HDDs to be a duplicate of the other, so that I have three copies of my most important files (on the internal laptop drive and on the two externals) and two copies of my less important media files (just on the two externals). What is the best way to create the duplicate external drive: by creating a RAID 1 set? or is it better to simply use Carbon Copy Cloner to backup to both drives separately?

    I'm quite the beginner in all of this, and would greatly appreciate some guidance. Thanks.
     
  3. itickings macrumors 6502a

    itickings

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    Apr 14, 2007
    #3
    I would personally try to only have one of the drives plugged in at a time and not both at the same time for most of the time. Would really suck to have a power surge or other failure corrupt both backups at once...

    Regarding the "less important media files" you intend to only host on the external drives, how often will those change? Do you need to have them constantly synchronized?

    How frequently do you intend to make backups?
     
  4. Evolvere thread starter macrumors member

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    York, UK
    #4
    Thanks for the reply.

    I was actually planning on buying either a surge protector or a UPS, but I see the extra protection of having the second drive unplugged. But do you know if a RAID 1 set is more susceptible to both drives being corrupted due to some sort of software failure rather than two separate drives that are simply cabled together? (And having done some more reading, it seems that a RAID 1 setup might be overkill as it's apparently primarily about eliminating down-time when one drive fails. I'm a student with some work and media to backup, down-time isn't an issue.)

    The "less important media files" refers mostly to my intention to backup my DVDs. There won't be much rapid change at all, and so I imagine a weekly backup to both drives would suffice. My important files are my university documents (which I also backup on a memory stick and online anyway) and my music collection, which again changes very slowly.

    I suppose all I really need to know now is, is Carbon Copy Cloner going to allow me to easily automate backups and sync the two external drives? I don't need a guide on how to do any of this, just some assurance that I can. I'm ready to read and learn once I have everything in place, I just want to know that I actually will have everything! ;)

    Thanks again itickings.
     
  5. itickings macrumors 6502a

    itickings

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    Apr 14, 2007
    #5
    Regarding RAID1, I've personally had an array of two drives rendered inaccessible due to corruption. On the plus side, they were identically corrupted, so the RAID1 obviously worked and kept the drives identical. It just wrote the wrong things to them. :p

    If you don't really need the drives to be identical at every single moment, I'd say that RAID1 adds more risks than benefits.

    I'm no CCC expert, so I can't answer that specific question, but from the specifications it looks like it would be useful.
     
  6. Evolvere thread starter macrumors member

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    #6
    That's bad luck with your array! But yes, I agree. I think in my case RAID 1 would be a bad idea. Two separate drives will be fine and safer. Just growing up with the Internet, you get to hear about this RAID thing, and so when I decided to get some extra storage I thought I should look into it.

    I'm going to delve into the documentation for CCC and see how it all works. I know there's SuperDuper to check out too. Probably order some drives next week some time once I'm all set.

    Thanks again for your help.
     
  7. itickings macrumors 6502a

    itickings

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    Apr 14, 2007
    #7
    RAID 1 is very useful in many situations, but not a silver bullet of any kind. It has saved considerable amount of time and money on multiple occasions on servers I've administered. Deal with a high enough number of drives, and failures are statistically certain...

    There is nothing wrong with RAID 1 for personal use either, of course, just that if the choice is between having only the RAID vs. one drive and a separate backup, I prefer the latter.

    Good luck!
     
  8. hamlinspahn macrumors regular

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    Apr 9, 2010
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    Oklahoma City
    #8
    Best Practices

    Question: how does business that has millions of dollars riding on their data do it.
    Answer: Raid and Tape Backup
    For you I would say raid and dvd or cd backup since tape systems are expensive. The software you use doesn't really matter if it backs up it backs up.
     
  9. Evolvere thread starter macrumors member

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    #9
    Fortunately I definitely don't have millions of dollars riding on my data! :p

    My most important files are already backed-up multiple times. Although I might as well burn them to a DVD as well just to be safe!

    And as for RAID 1, using it in my situation wouldn't give me any advantage over simply backing-up one drive onto the other. My data doesn't change fast enough to warrant it, and I believe I would suffer slower write speeds and potential corruption of both drives in the event of a software fault.

    But thanks for the input. I think I'm going to plump for an 1TB OWC Mercury Elite Pro Classic and a cheaper, slower USB drive for the backup drive.
     
  10. itickings macrumors 6502a

    itickings

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    Apr 14, 2007
    #10
    Just keep in mind that burned DVDs are notoriously unreliable for storage over time. But since you won't be using DVD as your only backup solution anyway, an additional copy won't hurt :)

    Storing checksums for files on a DVD backup is a really good idea, to make it easy to verify integrity. Of course, storing checksums for (supposedly) static files on hard drives might be interesting as well for backups.

    The drive strategy with one fast and one cheap one sounds good. Looks like you're all set.
     
  11. Evolvere thread starter macrumors member

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    #11
    I had only vaguely heard of checksums and had to quickly check on Wikipedia what they are exactly. I am right in thinking that they are basically used as an indication of when data should be re-backed-up, as it were? Are they easy to implement when storing data on a DVD?
     
  12. itickings macrumors 6502a

    itickings

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    Apr 14, 2007
    #12
    That's basically it, yeah. In this case, checksums are used to verify the integrity of files.

    For files that shouldn't change (like backups on a DVD), it is nice to have a way to automatically verify the intactness. It won't rescue the file, but at least let you know that a file is potentially damaged when you've restored it.

    How easy adding checksums for files depends entirely on the software and procedure used for burning the DVDs, it can be very easy and very hard. :)
     
  13. Evolvere thread starter macrumors member

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    #13
    Thanks for all your advice so far itickings. Could you point me in the direction of some software that would make the sumchecking "very easy"? ;)

    I'm not sure if I'll eventually use it but I'm ever curious to learn!

    And I'll post back once I've got my back-up setup in place. May be a couple of weeks yet as I've some essay and exam deadlines fast approaching unfortunately.
     

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