Raid 0?

Discussion in 'Mac Pro' started by xoggyux, Apr 1, 2009.

  1. xoggyux macrumors 6502

    Dec 4, 2008
    I have a question about raid 0. I have never done an array so I was wondering up to how many HDD I can config in raid 0 (stripped?, for better performance?) I was trying to find out in google but it says "two HDD" and I do not know if its two or more or just two... (I mean under the description I cannot see why it would not work with more) anyway Im planning to do this on a PC not in a MP but I guess its going to be exactly the same anyway thanks for help.
  2. OddThomas macrumors regular


    Apr 21, 2008
    Grapevine, TX
    with RAID0, the more HD you have, the faster. i currently have 3hd in RAID0. the one thing to remember is if 1 drive dies you loose everything. so backup the RAID0 drive. if you are just buying drives it is better to buy all the same drives.
  3. xoggyux thread starter macrumors 6502

    Dec 4, 2008
    thanks that was the answer I was looking for. regarding the backup issue, lets just say all my data is in external HDDs (to share easily among all my computers) and the important stuff is backed up, I will use it purely for the performance (I might use the space but as redundant etc) anyway I have another questions:

    you said:
    does that mean I can actually buy different (I mean, i thought that was a requirement no matter what, now I am wondering if I could do it with different HDD)

    what is the "optimum" number of HDD for an array (this is the issue, I was going to buy 3-4 1TB HDD for the array, but I could as well get 5-6 for the same price (640-750GB) the total storage will not be the same though, but if it offers better performance I'd rather do that, so will more drives is always better or after certain number it does not matter how many more you add the performance will remain the same.
  4. rylin macrumors 6502

    Aug 18, 2006
    What speeds do you need?
    IIRC, working with 10bit uncompressed 1080p requires ~230MB/sec.
    You should be able to get that with three drives (make it five to be totally safe, as speeds are slower depending on where you're writing).
  5. bzshutter macrumors newbie

    Mar 25, 2009
    Just for reference I have 3 WD RE3 320GB drives in RAID 0 for video editing scratch drive. I think 3 to 4 is a good number but if you don't need that speed 2 would be good enough to start with. For the same money, I'd get 3 smaller drives vs 2 large drives. Just remember , the bigger your RAID 0 array is, the more data you need to backup, or more data risk loosing.
  6. stiles macrumors member


    Apr 19, 2008
    I didn't want to start a new threat for this. Can you use time machine with Raid0? If so, then what is the disadvantage of using Raid0? I was thinking of getting a raptor for my boot drive and raiding 3 other western digitals, then backing up my raid via time machine. Has anyone tried something along these lines?
  7. hayduke macrumors 65816


    Mar 8, 2005
    is a state of mind.
    I currently have two Velociraptors in RAID 0 as a boot/users drive. This TMs to another internal drive. This seems like a reasonably safe mode of operation. Soon, however, I will add an internal system clone (SuperDuper) to the back-up scheme and a remote site back-up too (just got my data server today!!!).
  8. cmaier macrumors G4

    Jul 25, 2007
    Yes, you can use time machine. But that doesn't change the fact that for each drive you add to the array, the chance of failure goes up significantly (the likelihood of failure multiplies for each drive). And even if you have backups, having to replace drives, rebuild arrays, and restore all your stuff a couple times a year isn't a lot of fun.

    For example, if 1 drive has a 10% chance of failure in a given year, if you have a 2-drive array your chance of failure is something like 19%. 3-drives gets you to 28%, 4 drives to 37%, etc. (ignoring the additional possibility of multiple-drive failures).

    If you don't have enterprise-grade drives, the chances of a failure are, in my experience, pretty high - for example, I have two infrant raid boxes, running RAID 5. Each with four drives. I've had to replace a drive in one box or the other every year that I've had the boxes. With RAID 5, I didn't lose any data or have to do a restore, at least.
  9. nuckinfutz macrumors 603


    Jul 3, 2002
    Middle Earth
    I don't know why they call RAID-0 redundant because your data sure isn't.

    Hell with storage being cheap i'm not adverse to running RAID-10 (creating at least two mirrors and then striping them ).

    Be nice if I could do so on a QNAP TS-809. Take four 2-drive mirrors and stripe'em.
  10. rylin macrumors 6502

    Aug 18, 2006
    The problem with the silly QNAP machines is:
    Only two ethernet ports
    Cheap enough NICs that bonding yields lower performance.
    In other words, you'll get silly slow throughput out of hardware that really should be able to push more.
  11. Tesselator macrumors 601


    Jan 9, 2008
    Yes, you can. It's not recommended IMO!!! You're basically asking for the worst preforming drive to slow everything up. And I have experienced cases in the past where it actually wouldn't work at all because of an odd drive.

    Speed tops out on almost all controllers for SOHO (small office/home office) use at 5 drives in a level 0 RAID set - That would probably include Mac Pro's software RAID 0 too but there's only 4 connectors. :) Beyond 5 drives you get zero (or nearly zero) R/W speed increase but with some controllers you can get better bandwidth with more than 5. Some very good cards scale linearly all the way up to 8 drives. So for a busy file-server serving large data more than 5 might make sense but otherwise not.

    Also a lot depends on the drives you buy! What is the "fastest" HDD used as a single drive may or may not even be in the top 10 when working in a RAID. So try to find some RAID-0 tests on-line to see which ones are fast for RAID.

    You probably already know that the outer sectors of a drive are faster than the inner sectors. The same applies to a RAID array as well so it's beneficial in some cases to run a media test that scans across the entire platter and tells you how your drives profile and then to partition the RAID for those areas. Typical R/W speeds (averaged) for a 3 drive RAID-0 are like 250 MB/s. But for example, the three I have can achieve 400 MB/s (±20 MB/s) in the outer plater areas. So if I need to be assured of obtaining that kind of speed I can partition off the 1st 15% or so and have it. :) The inner-most portions of my platters can get as low 180 MB/s. And the middle 70% or so gets between 240 MB/s and 340 MB/s. That's with the drive's caches turned off and as a matter of note; any test software should never allow system cache to be used - as it's completely meaningless and absurd. :) I guess it can be fun though - I just wouldn't trust any test tool that allowed it. :p

    Also there's two kinds of tests. One os Random R/W and the other in Continuous R/W. Which is the most meaningful to you depends on what you use the RAID for. If it's video and sound editing then it's continuous. If you're a developer or doing DB stuff, etc. then Random. I'm a video and sound guy. :)

    Look around on Tom's Hardware site. There's 4 good (exhaustive) articles I know of on there about this very thing. They include benchmarks and explanation deeper than really possible here.


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