Mirrored RAID for boot drive?

Discussion in 'Mac Pro' started by elbirth, May 16, 2007.

  1. elbirth macrumors 65816

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    #1
    I just placed an order for an 8-core Mac Pro. I had originally decided to wait for Leopard, but with it being pushed back to October, I decided waiting another 5 months wasn't worth the hassle. Plus now it may be January before it's out, and I really need a good desktop machine to replace my MacBook Pro from being my everyday computer.

    Anyway, I'm wondering if anyone could tell me if it's much trouble put the boot drive in a mirrored RAID (RAID 1)? I just ordered the machine with the standard 250GB drive but will be ordering 2 500GB Seagate drives to use in it (I'll probably toss the 250GB in a FireWire enclosure). Since I'll have to reinstall OS X anyway, I'm wondering if I have to setup the RAID while installing, or if it can/should be done after the computer is up and running.

    I naturally don't want to take a big performance hit, but my understanding is that it's generally not too bad. Is this true? I won't be doing anything that requires the absolute fastest read/write speed possible, anyway. My reason behind wanting to do it is for data integrity. I have a 1.2TB fileserver set up that I'll be having the computer backup nightly to (or maybe just weekly if the RAID works out). However, that still leaves a window for data loss in case a drive fails between backups. With a RAID 1, I'd have a full copy on 2 drives and if one dies, I should have time to replace the dead one and not lose anything at all. Just another level of security, really.
     
  2. CanadaRAM macrumors G5

    CanadaRAM

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    #2
    Why do you want a mirror on your boot drive? Because you would be mirroring a whole bargeload of swap files writes, and precious little data that changes daily.

    Presumably you will be storing all of your data documents on a separate drive for the speed improvement of separating data from System and scratch files.

    I would just do a scheduled backup of the internal drive using SuperDuper or similar.

    If you want data protection, keep the 250 as your boot drive, and put your data files on a 500, mirrored by the other 500.
     
  3. elbirth thread starter macrumors 65816

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    #3
    well, I was thinking about mirroring the boot drive because I use the default documents, music, pictures, etc folders in my /Users/[username] directory. Is it possible to redirect the save location of those to another drive, or would I have to just create my own similar folder structure on the other drive?
     
  4. patrick0brien macrumors 68040

    patrick0brien

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    #4
    -elbirth

    Yes, you can redirect the media libraries to another drive. Which is good, because if you wish to Stripe, Mirror your boot volume w/o a hardware RAID controller, which will indeed be you default configuration - in fact I haven't heard of a harware RAID controller for this purpose - you will not be able to boot.

    Reason being is that you need to boot for the software RAID controller to mount and work.

    If you RAID your startup volume, you will create a chicken-and-egg situation: can't read RAID w/o booting software, can't read software, won't boot.
     
  5. elbirth thread starter macrumors 65816

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    #5
    how would I redirect the directories then? I've tried looking around in system preferences but haven't seen anything stand out
     
  6. patrick0brien macrumors 68040

    patrick0brien

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    #6
    -elbirth

    Well, depends on the app.

    iPhoto is easy - it even has the setting. Move your iPhoto Library to your drive of choice (it's in the "Photos" Folder - don't move that). When next you launch iPhoto, it'll ask where you library is - browse to it in it's new location, and you're done!

    iTunes needs a bit of fakery (and I'm a bit rusty here so it may take trial and error). Again move your iTunes library out of the Music folder to it's new location. But! Create an alias of the newly located iTunes and place it back into the Music folder, editing the name of the alias to just "iTunes". When next launched iTunes should be fooled.

    What else?
     
  7. elbirth thread starter macrumors 65816

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    #7
    Well, I was more or less looking at moving my user directory to a separate drive if possible, mainly so that the mirrored RAID would automatically create copies of my preference files and the like. I know those probably don't change often enough to *need* to be included in the RAIDed drive, but it's for the sake of completeness.

    Most of my every-day stuff is in subfolders of my Documents folder, so those would be simple to just relocate and not have any hassle. Although most of my email accounts are IMAP, I do have one POP account in Thunderbird, but that's simple enough to redirect in the account options.
     
  8. patrick0brien macrumors 68040

    patrick0brien

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    #8
    -elbirth

    Ok, let me save you a lot of pain then.

    Superduper is your answer - and it'll even make it bootable. See this posting: http://blog.sneezingfrog.com/2007/05/superduper.html

    My boot drives back themselves up every day at 7:30 in the morning.

    The advantage to this method is that should your primary ever fail, the next time you boot, the machine will be smart enough to go to the backup drive, and bingo.

    Also, with this method, unlike a RAID, doesn't require the drives to be the same size.
     
  9. elbirth thread starter macrumors 65816

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    #9
    I appreciate the suggestion, but that's actually not what I'm looking for. I already have my MacBook Pro (which I plan to carry over to my Mac Pro) do an incremental backup on a nightly basis at 3 am to a fileserver sitting on the network for the sole purpose of holding a backup in a RAID 5. So in a worst case scenario, I'd lose 24 hours of any new data if my computer died.

    My concern is backing up data throughout the day so I don't lose *any* data if a drive fails. Is that a bit excessive? Probably. But I've had a drive die before and even though on a normal basis anything lost would be negligible, I hate to lose *anything*.

    If I could simply have my /User/[username] folder on a drive other than my boot drive, I'd be set. Is that possible?
     
  10. patrick0brien macrumors 68040

    patrick0brien

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    #10
    -elbirth

    Not sure. I think you'll have to Google a bit for this.

    But, your specific needs are what Time Machine in Leopard is for - think you can risk <24hr loss of data until then?
     
  11. trainguy77 macrumors 68040

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    #11
    Well what i have done is used syslinks to connect every folder in my home folder to the other drives folder. You could do this same thing with the home folder if you wanted too. So just log in as root. Move your home folder to the external drive. Then create a syslink that you place back in the users folder. Then log in as your main user and it should be fine.
     
  12. elbirth thread starter macrumors 65816

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    #12
    Time Machine was one reason I had originally decided to wait until Leopard came out to get a Mac Pro (to avoid paying extra to upgrade instead of having it preinstalled). That'll probably end up being my best bet in the long run, since it seems like this could turn into quite a dilemma. Thanks for offering help, though!

    Hmm, that's not a bad idea. I'll look into that if I can't come up with anything else
     
  13. mkrishnan Moderator emeritus

    mkrishnan

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    #13
  14. slughead macrumors 68040

    slughead

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    #14
    I run a setup like that. I boot off a 10kRPM and my user folder is a 1TB RAID-0. I use netinfo instead of symlinking though.. I found symlinking to be dangerous.

    If I disconnect the RAID and boot, the user directory is recreated on the 10kRPM boot drive (/users/slughead) and it pretends its a fresh installation.

    All you have to do to fix it is logout, mount the drives, and log back in (usually). If that doesn't work then you just edit netinfo again, and everything works like it did before.

    I had this setup with my G5, I took my RAID and popped it into my Mac Pro, changed the netinfo, and bam! All my settings were transported to the new computer.

    I've had the same user folder on the same format of the same RAID for years now, on 2 computers!
     
  15. mkrishnan Moderator emeritus

    mkrishnan

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    #15
    That's kind of what I expected.... what exactly does using netinfo mean? I know that one danger with symbolic links is that the ownerships and permissions do not follow correctly. For instance, when users place their iTunes library in the /users/shared folder, they're strongly encouraged to implement an access control list on the linked folder so that it does not get ownership conflicts over time.

    Is there a guide to setting up something like this using netinfo instead of ln -fs?
     
  16. elbirth thread starter macrumors 65816

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    #16
    I'd really like to know how to do this as well, since it not only seems to be safer, but pretty much exactly what I need to do
     
  17. slughead macrumors 68040

    slughead

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    #17
    Netinfo is a sort of "registry" Apple uses for some specific things. After working with unix for the past 3 months, it's great to have it consolidated into 1 place.

    There's no guide that I know of, but I'll just write it here:
    1. open NetInfo Manager.app (/Applications/Utilities/NetInfo Manager.app)
    2. click on "users" in the middle column
    3. select your user shortname from the right column
    4. click the lock in the lower left (to make changes) and enter your admin password
    5. click on the 'home' field and edit it to be the path to your new home folder. DO NOT add a forwardslash (/) at the end, and remember to make it the absolute path--from the root of the hard drive (start with a forwardslash).
    Note: If you want your user to folder to be on another hard drive, start with /Volumes/[volume name]/path/to/folder.
    Example: My user folder is the RAID-0 with the name "Blarg", so my user folder path is /Volumes/Blarg
    6. Go into File: Save changes
    7. Logout

    Oh I forgot to mention: Make sure your user owns the folder you're making into your user folder (duh). If it's a separate volume, you can turn permissions off. Be careful though, sometimes it'll make your keychain password blank if you do the latter.

    Also, don't ever change the name of any ancestral folders without also modifying netinfo again. For instance, my user folder is on a drive called 'Blarg', if I change the volume name to 'Flarg', OS X will revert everything back. No data loss will occur if this happens, but I'll have to edit NetInfo again and fix it.

    As for symlinks, I remember using that method at first and many applications had a tough time figuring out what was going on. Perhaps they fixed this in 10.4.x but regardless, this netInfo one works great.
     
  18. soup4you2 macrumors regular

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    Apr 12, 2007
    #18
    I've done this before and it's rather simple actually.

    Basically have your login prompt set to ask for username and password. and goto the logon screen.

    enter >console as your username

    That will bring you out of the gui and into a console, from there

    mv /Volumes/Mac HD/Users /Volumes/Mac Raid/
    ln -s /Volumes/Mac Raid/Users /Volumes/Mac HD/Users


    Type exit a couple times to return to the login window and everything should work just fine. all the users directories will be on the raid device while the system is on the other. and it's completely seamless.
     
  19. mkrishnan Moderator emeritus

    mkrishnan

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    #19
    That's actually very straightforward, and it sounds like the explicitly correct way to do this! Thanks for the walkthrough!

    Can this system also be used to place the home drive on a served volume? Not that I'm going to run out and do it, but, say, if I had a Mac Mini or an iMac and a 1 TB volume on an AEBS, could I place my home directory on the AEBS?
     
  20. elbirth thread starter macrumors 65816

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    #20
    wow, thanks for the info guys. that looks like exactly what I need to do and is extremely straight forward

    now to get the computer and drives and get it all set up
     
  21. slughead macrumors 68040

    slughead

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    #21
    Maybe. The mounted network volume would have to be accessible through the freeBSD subsystem, instead of just the finder. Also, it would have to be mounted prior to login for obvious reasons.

    Honestly I've never tried it, sounds like a cool idea though.
     
  22. trainguy77 macrumors 68040

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    #22
    Yeah I use symlinks and they are fine. Maybe it was a change in 10.4 but your method is much easier. I am tempted to switch from using symlinks to your method...:rolleyes:
     

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