Redundant RAID 0 stripes and an optical bay SSD

Discussion in 'Mac Pro' started by iondot, Aug 26, 2010.

  1. iondot macrumors member

    Jun 30, 2008
    I am considering using two RAID 0 stripes consisting of two 2TB drives each. This would give me a 4TB of storage with 4TB set off for back up.

    However, I am very unversed in RAID systems and I have a feeling this may be a foolish configuration. Any thoughts or help would be appreciated.
  2. jav6454 macrumors P6


    Nov 14, 2007
    1 Geostationary Tower Plaza
    RAID 0 is not recommended for back-up drive setups. RAID 1 is.
  3. Pak^Man macrumors regular

    Jul 28, 2008
    Columbus, OH
    To expand on that.....

    RAID 0 = Speed (but risky as data is split up on two drives; doubling the probability of drive failure)

    RAID 1 = Redundancy (this is what you want for backups)

    All the best!
  4. iondot thread starter macrumors member

    Jun 30, 2008
    Raid 10?

    Is what I am describing above a RAID 10?
  5. alphaod macrumors Core


    Feb 9, 2008
    Hold a sec…

    Redundancy ≠ Backup.

    Redundancy sure means you have your data if a drive dies, it also means if you delete something, it can't be recovered. That's why you have a back up… to recover deletion.

    Anyways what you described is RAID 0+1: a mirror of stripes; RAID 10 is a stripe of mirrors.


    And what's your question about optical bay SSDs?
  6. iondot thread starter macrumors member

    Jun 30, 2008
    No question with regard to SSD's other than to note it as part of what I intended to set up. I'm old enough to have once lived in the world of SCSI interfaces and their voodoo like rules so it is mentioned out of caution. Not relevant unless it's relevant; if, for example, you could not do what I described with an SSD in the optical bay.

    In any event, it would appear what I've described could be set up as a RAID 10, or as two RAID 0 stripes, using the second for a time machine back up.
  7. dave-tx macrumors member

    Aug 8, 2007
    I'm currently booting off an SSD in SATA port #6 on my early-2008 MP. My four drive bays are used as two mirrored (RAID 1) file systems.

    As a side note (and completely unrelated anecdotal tale), it seems that my SATA port #5 was nonfunctional, and the machine is currently at the Apple store having its motherboard replaced (thank you AppleCare).
  8. Chaszmyr macrumors 601


    Aug 9, 2002
    In my opinion, the type of setup you're describing is undesirable. I have found RAID 0 to be pretty unreliable. You're thinking that you'll be safe from a drive failure, which is true, but both times I had a RAID 0 failure it was a controller failure, not a drive failure (first time it was a hardware controller, second time it was a software controller). With your setup, a controller failure would wipe out the data on all four of your drives.

    You might want to look into RAID 5 and/or using an external drive as a backup. I myself am a fan of Western Digital's external drives because they come in large capacities, they're reasonably priced, quiet, and I have five of them and none have failed yet (unlike my 3 LaCie drives, 2 of which failed).
  9. sboerup macrumors 6502

    Mar 8, 2009
    Yes, RAID1 does NOT equal a good backup system. It is only for system uptime. In my experience, RAID1 arrays are much more prone to data corruption than anything else. If one file is corrupt on drive1, then it will immediately be corrupt on drive2.

    When I normally have colleagues asking me about RAID setups, I will always steer them away from it because they don't know what they are getting into. If you want speed, then RAID0 is the way to go, but ALWAYS assume that the data on those drives will be wiped clean at any instance, so make sure it is constantly backed up.
  10. nanofrog macrumors G4

    May 6, 2008
    It would be foolish IMO, as a stripe set isn't as reliable as a single disk (one disk dies, all data is gone; and the single disk failure rate multiplies by the number of disks used in a stripe set).

    However, you can take all 4x disks and create a level 10 array. It offers 2x the speed as a single disk, at the cost of half the total disk capacity (added up) in order to allow for 2x disks to fail without data loss.

    How you do this (from Disk Utility):
    • Create a RAID 1 out of 2x disks
    • Repeat with the other 2x disks
    • Create a RAID 0 out of the 2x RAID 1 arrays you just made

    Reading up on the RAID wiki can provide more information if you're interested. ;)

    Please understand that RAID should not be used to replace primary data locations and backups, as things can and do go wrong (i.e. don't assume a RAID 1 is the same as a backup; it's not). It's possible to use one RAID as a backup for another, but they're not connected (automatic as RAID 1 would be, as any mistake made is duplicated without the user being aware of it; think accidentally deleted files...). So keep a backup of some kind, and use backup software to manage the data copying for you (Time Machine, Carbon Copy Cloner, or Super Duper).
  11. VirtualRain macrumors 603


    Aug 1, 2008
    Vancouver, BC
    But, if he only has 4 drives to work with, and has almost 4TB of data... then the only real option that provides him a backup solution is his original proposal. A 4 drive RAID 10 array is great if you have another set of drives for backup, but if not, then he's better off doing what he proposed even with the added chance of disk failure, at least he has a backup to guard against user error and he's covered if there's a single drive failure.
  12. nanofrog macrumors G4

    May 6, 2008
    Well, even in this configuration, the max data limit from what's been given can't be but 2TB (2TB per set). At any rate, I'm presuming that the capacity isn't critical, as it's not listed (4TB = max capacity of all 4x disks).

    I prefer to keep the backup risk above that of a stripe set, even if it's only n = 2 members. It's not uncommon for users to use identical drives, bought at the same time, and from the same source, which increases the risk of multiple failures if there's a bad batch (gets really ugly). Essentially a risk multiplier above the designed/implementation risk level.

    If it's budgetary, the risk needs to be well understood by the person using it, so they've motivation to increase the budget (wait, whatever) to get a good storage system in.

    I realize the 4x HDD bay limitation can cause problems (seems to happen often, going by the usual questions on RAID), as it usually forces users to buy external equipment. But I see it as part of the compromise of using a MP and OS X, and should be expected (assuming they've done their research or already know what they're doing). If not, there's probability they'll end up learning the hard way. :eek: :(
  13. StofUnited macrumors member

    Jul 30, 2010
    So Chaszmyr, I am wanting to setup RAID 0 for speed increase for some hobby video work I am doing so I can hopefully speed up some video connversions and make sure that i can do scratch on larger almost HD files.

    Sounds like the controller failures you are talking about are HUGE issues that destroy data on all HDDs. I guess I should start by just doing regular and if I have issues with speed then change it up - but I really want to try RAID 0. I will have all data backed up on external drives - but to lose all my data on all 4 HDDs would really suck.
  14. Honumaui macrumors 6502a

    Apr 18, 2008
    Chaszmyr very curious what brand of controller hosed your data ?
    and when you say software hosed you ? how did that happen ? not doubting you just I have found it is usually something that can be avoided ?

    usually I hear of people with on board raid having issues or talking about their highpoint and thats enough to know DANGER WILL ROBINSON !!!!
  15. VirtualRain macrumors 603


    Aug 1, 2008
    Vancouver, BC
    Not to diminish or down-play Chaszmyr's experience, but RAID0 is very reliable and not risky. Sure the chance of a failure is a function of the number of drives in the array, but that's still a remote risk. And, if you backup, the impact of a failure is simply the time it takes to do a restore.

    Personally, I've run RAID0 arrays in a variety of computers, with different chipsets and controllers, under Windows and OSX, for the last 10 years, and I've never had a data loss issue (knock on wood) but I also backup. In fact, I've never had a drive failure or RAID data corruption issue that caused me to use my backup.

    I'm not saying it can't happen... it clearly does, but it shouldn't keep you from utilizing it... as long as you have a backup strategy or are prepared to rebuild from scratch in the event of a failure (which is actually an acceptable strategy if you're simply running OS/Apps on your RAID array and can deal with the added down time).
  16. nanofrog macrumors G4

    May 6, 2008
    Granted, the failure rate is a worst case scenario (n units * that of a single disk), but given the differences in drives (consumer v. enterprise) and Quality Control (i.e. 10 - 13% DOA rates), the risk is quite real. Putting an exact value to it is hard though, as you also have to take the exact usage into account.

    SSD's have a high reliability potential for reads, but not so much for writes right now (MLC based disks). SLC is fine, but awfully expensive still.

    As per recovering a stripe set, it's not a good idea to discount the potential time consumption for re-performing lost work (i.e. data generated between the last backup and time of failure can be extensive). With a good backup strategy (i.e. frequency of incremental backups), this will be reduced, but can't be eliminated completely.

    All that said, if a user has a good backup system in place, and understands the compromises involved, can proceed with it if they're willing to accept them.
  17. iondot thread starter macrumors member

    Jun 30, 2008
    Does "Time Machine", in your opinion, offer a good backup solution?
  18. Honumaui macrumors 6502a

    Apr 18, 2008
    not had issues with Raid 0 ? I think its fine and safe and a good option for some things and Raid 0 on the mac has always been good for me !

    work files for your living is not one of them !!!!
    scratch yes ! video importing and or some other stuff ? I guess
    play around hobby and want the speed ? sure

    then again I have insurance on my place ! raid 0 for work is like buying a house then not insuring it !

    Cheap hardware like Highpoint seems to have issues ? I did back in the G5 days with them !!!!

    or I hear some say well my onboard raid built into my MB !! and well that usually tells me how things are going to come out :)

    like I said above usually it always boils down to something else ? very rarely on high quality proper setup stuff is it some mystery thing ?
    HDD dies ?
    controllers can die ? but rare
    mystery things are usually a human error of some kind ?
  19. nanofrog macrumors G4

    May 6, 2008
    Time Machine is just backup software (location and scheduling). I meant in terms of both the hardware (single disk, external enclosure,...) as well as keeping the scheduling short enough to minimize your risk of "lost" data.

    But as backup software goes, TM does work (it can be difficult to make settings other than the defaults, but it's possible to do).
  20. iondot thread starter macrumors member

    Jun 30, 2008
    For now, I've gone with two internal 1TB Caviar Black drives for a RAID 0, backed up to a 2TB Hitachi 7K2000 internal drive via Time Machine.

    My last internal slot currently has an older 1TB Seagate backed up to an external 1TB G-TECH dive via SuperDuber. I expect to upgrade this part of the set-up to a 2TB in the near future.

    This seems relatively safe to me, but perhaps there are dangers I'm not aware of?
  21. philipma1957 macrumors 603


    Apr 13, 2010
    Howell, New Jersey
    well if your pair of 1tb caviar blacks in raid0 crash.

    time machine is a pain at times. I would want a second backup of them (along with time machine) use superduper and clone them onto an external esata drive like this one.

    I have seen this for under 110 shipped. it is bootable has its own power source and works well as a secondary backup. it can be detached and placed in a safe place. it can be set up as a boot drive and moved from MP to another mp. you can have a low cost esata slot added from owc to your mini.
  22. iondot thread starter macrumors member

    Jun 30, 2008
    If my pair of 1TB caviar Blacks crash, why wouldn't I restore them from the Hitatchi 2TB Time Machine backup?

    If Time Machine is problematic, am I better off doing a nightly update with SuperDuper?
  23. philipma1957 macrumors 603


    Apr 13, 2010
    Howell, New Jersey
    if you do time machine it is automatic (good). it is not bootable and restore can be time consuming. (neg)

    a plus and a neg.

    if you use a pair of 2tb esata plugin externals in a weekly rotation they would be bootable that means less down time. ( plus) .

    not automatic and tend to have a time gap one at backup a week.. ( neg).

    of course if you buy superduper it is low cost and allows setting your backup 1 time a week or more often then that. (plus).

    Having 2 backup systems for those caviar black raid0 is low cost in your case. Since they are not huge at 2tb. A 2tb raid0 is far easier to protect then an 8gb raid0.

    I looked at your website looks like nice work. since most of your stuff will be on the 2tb raid0 why not have 2 backups at a pretty low cost under 500 for sure,.
  24. Honumaui macrumors 6502a

    Apr 18, 2008
    my thought for a machine that you make a living on

    try to have a BU in place that is near the speed of your main storage and one you can quickly jump to and finish up the jobs you need to till the new HDD arrive to fix things !
    time machine is good to go back in time :) for a file etc.. you might need dif revision etc..

    but the other layer should be a working one that wont cripple you having a HDD with your main storage die is going to be stress enough then having to try to find something to put your files on and continue working etc.. is going to ad more stress !!
    best would be a choose a dif drive to get your stuff off and keep going
  25. jwestpro macrumors member

    Aug 12, 2010
    so, it sounds like my plan to use 4 bays with 4x 100gb ssd drives, stripe paired for speed and then mirrored is good speed and also data protection. these 4 are only for short term storage/working space as all work will then be copied off to esata two spaces as well, then later copied again to similar setup in another location.

    so with this my optical bay will separately hold a 200gb boot drive that i can have either mirrored to a 2nd one below it or onto a 2T miscellaneous space that could be partitioned into 200gb for optional boot and the rest for music or personal junk

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