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Backup, mirrored hard drives, RAID

Discussion in 'Recording' started by vividsonics, Jul 27, 2005.

  1. vividsonics

    vividsonics Guest

    Howdy folks,

    After reading this thread: (Dead Link Removed) I thought I should get on the ball with some storage technicques I've been wondering about. I have a few questions. I'm using a Powermac G5 single 1.6 GHz with 2 internal SATA drives. I use one drive for the system and programs (mostly DP and Reason) and the other to store samples. I'm using a Firewire 400 drive for my audio (multi track sessions).

    What exactly is a RAID array? How would one set this up?

    I've heard of having a "Mirror" drive where everything written to one drive is duplicated to another drive for backup in case one drive fails. How would I go about setting this up?

    Thanks for your help.
  2. hociman

    hociman Active Member


    A RAID array is a group of disks that appear as one to the OS. If you had a 2nd firewire drive that was the same model and capacity as the first, you could set the two up as a RAID using Apple's Disk Utility. I forget the exact steps, but that is where you would do it.

    By using multiple disks to appear as one volume, data gets written across multiple disks, which in theory increases throughput to the RAID array.
  3. Big_D

    Big_D Well-Known Member

    What Hociman is talking about is a striped array. This is where data is spread across 2 or more drives to increase through put since all drives can be read from at the same time but will appear to the OS as 1 large drive (the combined size of both drives). This is known as RAID 0.

    You are asking about a mirrored array, RAID 1. This is where 2 "identical" drives are used to create identical data sets on each drive. It appears to the OS as 1 drive but only the size of 1 of the pair. If a drive should fail or the array gets out of sync the computer will run off of the 1 drive until the array is rebuilt.

    RAID 0 provides no such protection, if the above happens you loose everything. RAID 0 is not recommended for DAWs. If you feel the need for RAID 0 in a DAW I would suggest RAID 0+1. It provides the performance of striping with the saftey of mirroring but requires 4 "identical" drives.

    RAID 1 would be a good choice for you as it provides solid backup. I'm not familiar with Apples RAID implementation so I would suggest a visit to an Apple forum.
  4. hociman

    hociman Active Member


    Disk Utility only allows you to create one RAID per bus or channel. So if you had a dual channel SCSI card, you could have 2 RAIDs. If you have 2 ATA buses (MDD G4s), you could have 2 RAIDs.

    I setup a striped RAID on an OS X Server and then set Carbon Copy Cloner to clone the one RAID ot the other. This allowed me to, effectively, have a mirrored RAID (level 1) while using Disk Utility to create a striped RAID (level 0).
  5. TheArchitect

    TheArchitect Active Member

    Raid (and mirroring especially) should not be considered a backup methodolgy. With those arrangements if a file corrupts or is deleted, the corruption/deletion is replicated to the redundant drive. You will still need a backup/archive plan in place.
  6. hociman

    hociman Active Member

    time is on my side

    In my situation, the mirror takes place once a week, so I have 6 days to realize something is deleted and replace it. I also have Carbon Copy Cloner configured to not erase files already on the mirror.

    Point noted though that if you backup a corrupt file, you are screwed.
  7. TheArchitect

    TheArchitect Active Member

    Re: time is on my side

    You are not doing mirroring in the traditional sense then. You are just copying files to another disk once a week. True mirroring happens in real time.
  8. hociman

    hociman Active Member

    Re: time is on my side

    True. For the record, I did say that my setup effectively did mirroring. That might not have been the correct word, but my point was that in the end I had a mirror.
  9. Big_D

    Big_D Well-Known Member

    While it's true that Mirroring should not be your only means of backup I'm curious as to why you say "mirroring especially". Your not suggesting stripe would be better are you?

    You are partially correct in that deletions would be carried out on both drives but corrupt data is a different story. It all depends on where the corruption of the data takes place. If it's in the processing of the data it would indeed be written to both drives but if as in most cases it becomes corrupt on the drive itself (ie. bad sectors, head crashes etc.) the data on the other drive would survive. By simply rebuilding the array and copying the data from the good drive your original data would be alive and well on both drives.

    I do agree an archival plan is needed for backup and mirroring should not be your only means but it does have it's place. One of the keys to a great DAW is unfailing performance and mirroring can help provide that. If you're in the middle of a recording session and your audio drive fails you're dead in the water and archival drives don't help here. With mirrored audio drives you just keep on going as if nothing ever happened, and not so much as a single millisecond of audio will be lost. Not bad for the price of a second drive and a few minutes time huh.

    Really anyone who records audio for a living should do this along with an archival backup. Or you could just explain to your clients that the session is lost when it happens to you.
  10. TheArchitect

    TheArchitect Active Member

    Honestly, not sure why I threw that disclaimer on there. I am certainly not intending to suggest striping is better. In some ways its actually worse. True, with mirroring you can continue as if nothing happened but you better know how to recover it or its a pointless excercise. I've had many clients screw up the recovery and lose everything anyway. As for striping, true you can continue but you will take a big performance hit when it needs to read data that was on the failed drive from the redundant area.

    The best way to do it would be dual hardware raid controllers configured for mirroring and the two arrays mirrored by the OS. This way you are protected both from disk failure and controller failure

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