An Explanation of RAID Levels [u]

Posted on by Larry

[ This article was first published in the July, 2009, issue of Larry Jordan’s Edit Smarter Newsletter.  Updated August, 2014, and July, 2017 (for SSDs). ]

RAIDs (Redundant Array of Independent Disks/Drives/Devices) consist of a number of hard drives or SSDs grouped together into a single unit so that they appear to the computer as a single device. Because there is more than one hard drive in a RAID, they offer greater performance and storage.

There are different levels of RAIDs, identified by numbers:

RAID 0 – Fast, inexpensive, no data redundancy. Requires a minimum of two hard drives inside the RAID enclosure. The more drives you add, the faster the performance, as performance and storage capacity are the sum of all drives in the RAID. However, if you lose one drive, you’ve lost ALL your data. Most often used when speed combined with low cost are paramount.

 

RAID 1 – Complete data redundancy. Generally only uses two hard drives inside the RAID enclosure. Often called “mirroring,” each drive is a complete copy of the other. Most often used for backing up servers or when on-set for DIT media work. Has the speed and capacity of the slowest single drive in the system.

 

RAID 3 – Medium-fast, data redundancy. Requires a minimum of three drives, as one drive is reserved solely for parity data. Should one drive die, your data is safe. This technology is no longer in common use,  replaced by the faster performance of RAID 4 or 5 systems.

 

RAID 4 – Very-fast, data redundancy. Similar to RAID 3, requires a minimum of three drives, as one drive is reserved solely for parity data. Should one drive die, your data is safe. This is the preferred RAID format for SSD drives because of how the data is stored on the drives. When compared to a RAID 5, RAID 4 with SSDs is about 25% faster on reads.

 

RAID 5 – Very fast, data redundancy. Requires a minimum of three drives and shares parity data across all drives. Most often found with four or more drives inside. If one drive goes down, your data is safe. This is the preferred choice for RAIDs containing spinning media (traditional hard disks). Used for both locally-attached storage and servers.

 

RAID 6 – Fast, extra data redundancy. Requires a minimum of four drives. This version protects your data in the event two hard drives die at the same time. More expensive than RAID 5, but, generally, the same physical size. Like the RAID 5 this is most often used connected to just one computer. Not as fast as a RAID 5.

 

RAID 10 (or 1+0) – VERY fast, totally redundant. Requires a minimum of four drives, but is more often created by combining two matched RAID 0’s into a RAID 1. This provides the speed equivalent of a RAID 0, with the data redundancy of RAID 1. As RAIDs continue to drop in price, this can be a less-expensive way to create systems that rival the performance of a RAID 50.

 

RAID 50 – VERY fast, data redundancy. Generally the domain of very large RAIDs, this format combines the speed of RAID 0 with the redundancy of RAID 5 by dividing the RAID into sections, where you can lose a drive in each section without losing data. These systems generally cost more than $10,000 and contain at least twelve drives. Generally used in network and server situations where multiple users need to access the same data.

 

RAID 60 – VERY fast, extra data redundancy. Generally the domain of very large RAIDs, this format combines the speed of RAID 0 with the redundancy of RAID 5 by dividing the RAID into sections, where you can lose two drives in each section without losing data. These systems generally cost more than $10,000 and contain at least twelve drives. Generally used in network and server situations where multiple users need to access the same data.

 


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12 Responses to An Explanation of RAID Levels [u]

  1. Pingback: Raid explaination | Bebrossers

  2. Tim Jones says:

    A couple of deeper points –

    You need a hardware controller for RAID 5 (I recommend ATTO Tech for the best level of compatibility), so you’ll also need an external chassis for the drives. Apple’s software RAID support only supports RAID 0. I don’t recommend Apple’s Mac Pro RAID card for all of the reasons that people complain about on Apple’s forums.

    As Larry mentions, the performance of your array is based on the drive speed, so if you’re going to use the extra drive bays inside your Mac Pro, use all three of them for this array. And don’t “cheap out” on the drives. Consumer-grade drives are very inexpensive right now, but hard drives are a perfect example of the adage “you get what you pay for.” Spend the extra money for enterprise-class drives and you’ll have the best performance and the longest life available. Also, be sure they are 7200RPM rather than 5400RPM drives. This way, you’ll easily see ~300MB/sec of sustainable read and write speed using Apple’s software RAID 0. We use Seagate’s Constellation class drives in stripe mode in all of our Mac Pros for performance and capacity.

    Also remember, RAID is NOT a replacement for backup and definitely not good for project archival. It’s good for drive failures (RAID 0 or RAID 5), but it won’t help with user errors like mistakenly overwriting or deleting files. A second set of disks – or better, an LTO tape drive – will allow you to recover a lost file.

  3. kenackr says:

    While I do consider myself “techy” and do possess a Computer Science degree, I still get gobsmacked with many of the tech advances in today’s ever changing world.

    I have known and been aware of the fact that data transfer rate between the hard drive & the CPU has been the boat anchor dragging down overall system performance when it comes to video editing. The raid concept is one answer to increasing data transfer rate and the explanation given above is clear & concise. No Problem there.

    I’ve been using 4 x WD 7200 rpm enterprise internal drives in my Mac Pro early 2009 4,1, but I’m only working with DV at present. No Problem there. I’m using 32 gig of all identical ram in the Mac Pro and upgraded the graphics card to EVGA’s Nvidia GTX680 classified GPU with 4 gig of ram. No Problem there.

    I’m finally going to move, kicking & screaming, into the Hi Def world where file sizes are significantly larger in the next 6 months. This prompts me to wonder about using WD 10,000 rpm 1 TB Velociraptors in a raid configuration and now we come to the point where I’m gobsmacked.

    Recognizing that my Mac Pro is built as a Sata II machine, but current drives are now made under the Sata III classification with a higher data transfer rate capability, I thought I’d need a Sata III pcie bus controller card to tap into the higher data transfer rate capability. When I posed the question to the big dogs on Apple forums, I was told,”no, you don’t need the Sata III controller” .

    Gobsmacked 1) Can I do a 4 drive Velociraptor internal raid level 5 in my Mac Pro? My thinking is to keep the drives as physically close to the pcie buss as possible because it’s the pipe line to the CPU.

    Gobsmacked 2) I assume the Mac Pro internal drive back plane is fed by the factory installed Sata II controller. Is this going to matter from a data transfer rate standpoint?

    Gobsmacked 3) Tim Jones notes that a controller card will be needed (I agree with his assessment of Apple’s software raid & their controller card), and quickly states that an external chassis will be needed. How does this square with the a dive I recieved for the Apple forums that no card is needed?

  4. Tim Jones says:

    Some quick answers –

    2 – while it’s not going to matter in light of your questions 1 & 3, SATA III drives are backwards compatible with SATA II signal paths.

    1 & 3 – No, you can’t RAID 5 inside the Mac Pro chassis without Apple’s little sidecar card because there’s no way to tie the secondary PCIe RAID card to the internal drive bus. And the note you received from the Apple forums is simply wrong. You can only Mirror, Concatenate, and Stripe under Disk Utility; no RAID 5 or 6.

    However, you really won’t see a performance difference by running the drives internally versus externally off of the PCIe bus and the ATTO R680 and it will make your Mac Pro run hotter (meaning louder fan noise). Plus, by going external, you can expand far beyond 4 drives. By going external, you can start off with something like the this Sans Digital box – http://eshop.macsales.com/item/Sans%20Digital/TR4XBNC/ for a very reasonable $270 plus drives and then add on lots more storage. Because of the manner in which SAS works, you can achieve sustained throughput speeds of over 600MB/sec with 4 drives or 1.2GB/sec with 8 drives (800MB/sec max with a Thunderbolt 1 connection).

    • Tim Jones says:

      Semantics, but yes, striping and mirroring are technically RAID levels, but we’re discussing RAID 5 ot RAID 6 in this instance. Neither of those are supported in Disk Utility.

  5. David says:

    Does anyone know if it is safe to edit directly off of a RAID set up? I typically just use my RAID system for backing up, but occasionally I need to open up an archived project and do a bit of editing in the project (and exporting as well).

  6. This is a fantastic blog ! I am glad i find someone who knows a lot about video technology.
    I have a question:

    I own a Mac Pro late 2010. I have a RAID external eSATA with 5 drives inside the box. I have been editing H.264 material and everything works just great. However, I have just purchased a Sony F3 and planning on shooting RGB 10 bits Slog to get advantage of the camera capability (i spend a lot of time doing color grading and needed that extra latitude). My questions are:

    1. would you record Pro Res 4444 RGB or you wouldn’t bother and record instead 4.2.2 HQ onto an external recorder (such as the Odyssey 7) ?
    2. Will my current computer RAID handle the data flow or shall i sell it and buy a new mac instead ?
    3. If my current RAID is not up to the task, would installing internal WD 10Krpm will make a difference ?

    Obviously, i gave up the possibility of shooting DPX files (too large for my computer to handle).

    Thank you

    • Larry says:

      Soufian:

      Thanks for writing.

      1. You get the highest color quality with ProRes 4444. If you bought the camera to improve your color, I would opt for this codec. And, yes, record everything to the RAID.

      2. As long as you are not doing multicam work, your RAID should be fine.

      3. Installing a single, internal drive would be FAR slower than your RAID.

      Larry

      • Thank you for the quick reply Larry.

        3. “Installing a single….” I forgot to mention what if there were all four inside the internal bay 10rpm fast drive. Would it result in a notifiable faster solution to edit those 4444 pro res files ? By the way, when recording into the upcoming Odyssey 7 (convergent design is waiting for apple approval along other minor things), at what stage do I select my color gamut (RGB or YUV) ? Prior or Post recording ?

        Thank you

  7. Pingback: Hard Drive Basics | Larry Store

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