Disk Utility Mirrored RAID Questions

Discussion in 'Mac Pro' started by OSXconvert, Oct 21, 2010.

  1. OSXconvert macrumors member

    Apr 11, 2002
    Brooklyn, NY

    I'm hoping the Mac Pro forum is good place to ask these questions. I've set up a 2-drive mirrored RAID in my external FirmTek 4-drive esata enclosure. The RAID was set up with Disk Utility and consists of 2 x 1TB drives.

    What I would like to know is how to swap out one of the drives and put in a replacement drive, a step-by-step process (i.e. "eject the raid from the desktop, turn off the power to the external enclosure, swap out drives, turn on power, use disk utility, etc., etc.). I'm not sure if the drives are hotswappable, if I do it all while disk utility is running, or what. My goal is to do this once a month so I always have one spare data copy in case something terrible happened to both drives in the external RAID.

    Another question: Will the single drive removed from the pair function just like a stand alone drive if I attach it to another computer? I assume so.

    Also, while I've heard that I should be running a separate back-up system as well (I use Time Machine to a 2tb drive), I'm curious whether rebuilding a mirrored raid is more or less time intensive than just doing a drag copy of all the content to another drive. I really don't care which method I use, swapping out a mirror raid spare or just copying to another drive, just would like to know which requires less time and babysitting.

    And finally, forgive my ignorance, but if I end up getting a spare swapping system going with the mirrored raid, I assume that the spare with previous data on it gets totally wiped when I put it back in again, that the rebuilding process is "not smart," meaning that even if very little of the data has changed since the last swap out, the whole drive has to be wiped and rewritten from scratch?

    Thanks for your help.

  2. nanofrog macrumors G4

    May 6, 2008
    Skip the swapping methodology you're trying to do. The whole point of a Mirror is so that if a drive dies, the other will take it's place without having to shutdown the system (meant for high availablility = 24/7 operation; it's why RAID 1/ mirrors are used for OS/applications locations for servers.

    Just use software to manage your backup (Time Machine), and if you want, keep a spare drive on hand, so that if you do have a drive die, you can replace it. The array will rebuild automatically.

    If you're still paranoid, you can toss on another separate disk via an external enclosure if you wish and make a clone of the OS on a regular basis.

    As per hot swap capability, IIRC, the FirmTek card does have it, but check their site to see if it does (has to be included in the drivers, as it's not supported under OS X Client Editions; it is for the Server Edition of OS X).

    But I have to ask... why a mirror?
  3. OSXconvert thread starter macrumors member

    Apr 11, 2002
    Brooklyn, NY
    Sorry for the delayed reply--just got busy...

    Well, maybe I'm using the wrong strategy. You tell me if it is overkill. This is my photo archive, scans and digital files of personal and client data, which I access a few times a week and edit to as well. I don't have it on all of the time, just when I need it. It is very valuable data. I have an offsite backup which is a clone, but wanted to do the safest, affordable data protection while I use it, so that's why I set up a mirror.

    My main worry is theft/fire/act of god at my studio, not a hardware failure, though that too I'd like to avoid. My goal is to find an easy system that requires a minimum of fuss. My thoughts were just that once a month or so at the end of the day when I'm done using the raided archive, I could just swap out one of the drives, take that drive home, and when I arrived the next morning, the mirror would be rebuilt and I wouldn't have to do anything else. Of course I could just clone instead, not really that much more hassle, though my spare drive idea, it seems to me is more elegant. Correct me if I'm wrong.

    I haven't done an experiment on speed, but I have a hunch that cloning a 1TB drive is much quicker than rebuilding a 1TB RAID mirror drive. If it gets done by the time I come in the next morning, I don't care which method I use.

    I love Time Machine, but I already have it running on a 2Tb drive for my day-to-day drives and there is not enough room to handle this photo archive as well. If there was some easy way to have multiple time machine backups going to separate backup drives I'd do it.
  4. nanofrog macrumors G4

    May 6, 2008
    What kind of throughputs do you require?

    Given the first post, I had the impression you're dealing with Photoshop and related applications, which benefit from additional throughput than that of a single disk.

    If this isn't the case, then a RAID 1 + on-site + off-site backups are fine for critical data. Even keeping the on-site backup disk/s in a fire restant safe might be something to think about.

    A mirror isn't really meant for this (it's meant to remain in the system at all times for avialability = system still works/data's available if a disk fails; which is why it's most commonly used for OS/applications in servers), but the clone would be fine for this type of intent.

    As per the rebuilding time of a mirror, it's not that slow (assuming no load on the drives other than the rebuilding). The throughput in such an event is ~ that of a single disk. There's a bit of overhead on the system, but it's not that much. It's when the drive is still in use during a rebuild that it will drag, as system access is given priority (that's what it's designed for).

    Time Machine is capable of fine tuning, though I've been told it's not easy to get it set.

    You could do something like an eSATA card + PM enclosure (usually found in 4, 5, 8 and 10 bay versions; there are also 2 bay units, but aren't all that useful IMO, as it's quickly outgrown).

    Software wise, you could take a look at Super Duper or Carbon Copy Cloner as a means for managing your backups (easier according to those that use it).
  5. OSXconvert thread starter macrumors member

    Apr 11, 2002
    Brooklyn, NY
    Speed is always important, but since I'm not accessing these that often and usually only to read data, it's not critical. Safety of the data is the most important thing for me. So I think what I'll do is just keep the mirror and schedule weekly clones via Super Duper to an external disk which I'll store offsite between uses.

    Thanks for all your advice, nanofrog.
  6. nanofrog macrumors G4

    May 6, 2008
    :cool: NP. :)

    Given the clarification as to what you're doing, you should be fine (do consider an off-site service though, as it covers you from "Act of God" events, such as fire, flood, lightning strike that any protection devices can't handle, ...). It's slow (primary backup or full restoration), but your data will still be in tact if something like that actually happens (and it's gotten cheap enough that it's even viable for home users to keep things like family photos and home movies = irreplacable).

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