RAID 3 possible?

Discussion in 'Mac Accessories' started by Desprez, Oct 13, 2005.

  1. Desprez macrumors newbie

    Oct 13, 2005
    Well, I'm not sure if this is the best place to pose this question, but I anticipate that the primary machine accessing this array will be my powerbook. If anyone can recommend a different forum, I'm open to ideas.

    I'm looking to create a RAID using 5 x 250GB external firewire drives connected through a firewire hub.

    I'd like to go with RAID 3. (Less CPU intensive than RAID 5) I can get the firewire drives for $160 apiece (anyone find a better deal?), so theoretically, this setup will give me 1TB for $800. (+ tax and the hub <$1000. I'm not planning on spending $5000 on an xserve solution!)

    However, I can't seem to find any software that will do RAID 3 or 5 for the mac, and the PCI solutions aren't going to work too well on a powerbook. (Disk Utility only does RAID 0 and 1, and going RAID 1 will end up costing about 50% more.)

    Unless my research has caused me to misunderstand how a RAID setup works, this seems to be a good bang for the buck. Seeing as most raid enclosures cost $300-$1500 for 4 or 5 bays not including the disks and or controlers, it seems cheaper to just get several external drives and run them in software since i'm more interested in the recoverability aspects than speed anyway.

    Does anyone know of any software than will run RAID 3? Is what I describe possible?
  2. CanadaRAM macrumors G5


    Oct 11, 2004
    On the Left Coast - Victoria BC Canada
    Running a RAID through a single Firewire port/controller (which is what you will be doing by using a hub) will limit your bandwidth to the speed of that connection. Much better to get 2 or more separate controller channels happening (PCMCIA Firewire 800 card in a Powerbook 15" or 17").

    For RAID 3 or 5, you may have to go to an outboard hardware RAID solution, don''t know.

    Go to and and do some reading.
    Barefeats is enamoured of the synthetic Xbench benchmarks, which may bear little resemblence to real life. Read the parts of storagereview where they analyze the performance of RAIDs for desktop use and conclude that there is little or no net performance improvement for single-user uses other than digital media creation (HD video).

    Ask yourself the question -- what are you doing on the Powerbook that would truly benefit from faster disk access? And then, how much additional performance are you really going to net?
  3. csubear macrumors 6502a


    Aug 22, 2003
    I wasn't aware that any one used raid 3. I personally have a 4 disk software raid 5 in linux. Works very well, CPU useage is not really a problem. Its a simaple parity XOR....

    If you want to use OS X for this, then i think the new 10.4 disk utillity does raid 5. I don't know fow i feel about it though, I havn't research it. I feel much better in linux. I know, and have used raid some recovery tools that saved my butt.

    As for useing it with your laptop, i would discourage that. Who knows what OS X would do if you uncleanly dismount those drives..

    As i see it you have two options

    a) cheap mac (a mini or something) w/ 10.4
    b) a cheap pc (p3 or better) w/ linux and raidtools
    c) a cheap pc w/ a nice raid card.. w/ linux or freebsd. 3ware makes some very nice raid 5 cards, but cost some cash.

    here is a guide to linux software raid

    considering that you aleardy spend 500-600 on harddrives, a cheap pc won't be too much more. if you go this route, make sure you get a big case w/ good airflow, and some PCI ATA cards. each drive will need its own ATA bus. You can not do the master/slave thing with RAID, really messes things up.

  4. Desprez thread starter macrumors newbie

    Oct 13, 2005
    I want RAID for the recoverability, not the speed.

    I'll check out those links you mentioned.

    I haven't spent anything yet. Always research first!

    Speaking of research, I managed to do some more digging. It seems that firewire isn't really an option as I originaly concieved. I would need to build a solution from scratch to keep the cost down. (there's kits to build the box, sans controler)

    My earlier research seemed to indicate that RAID 3 would have less CPU overhead than RAID 5. But if I'm going to get a hardware controller, this isn't an issue anymore.
    And if I build it, I'll have to get a controler.
    But the ones that do RAID 5 seem to mostly be PCI-X. Not an option on any of my older systems.

    Are there any PCI RAID 5 controlers that would work on an old G4 Tower (DVI)? I didn't come across any.

    More and more, it looks like the cheapest solution will be to set up a cheap dedicated machine for the purpose. Just like you suggested.

    I'd love to get more into linux... but I haven't been able to grok it yet. Time is a factor. Maybe this project will be the excuse to get going on that.
  5. superbovine macrumors 68030


    Nov 7, 2003
    Dell / EMC CX series SANS all support raid 3 in hardware. however, that is probably the only raid 3 SANS i have ever seen. there are probably a few scsi cards that support it as well. check adaptec and lsi. i am sure one of those are the card supplier to dell.

    edit: correction the lowest end model doesn't not support raid 3, but everything else in the cx series does.
  6. csubear macrumors 6502a


    Aug 22, 2003
    From the research i did a year ago:

    good hardware raid cards are expensive >300 or >1000 depending on how many ATA or SATA channels you need.

    crappy (as in have fun rebuilding when a drive drops out) "hardware" (checksums are done in software, so they are just glorified ATA controllers w/ software raid drivers) are cheap (~100-200).

    there are not many, if any, pci hardware raid cards with OS X drivers.

    These three things lead me to putting together a cheap pc, and install linux for a software raid 5.

    I spent: (a year ago)

    old p3 motherboard ($40)
    1GHZ p3 ($20)
    128mb pc 133 RAM ($15)
    10/100 network card ($5)
    old agp (voodoo 3) ($10)
    1 really big case ($75)
    400W ATX power supply ($50)
    Fans ($40)
    2 ATA 133 cards ($75)
    4 x 250GB ATA 133 drives ($600)

    for a total $930 and with 698 GB of usable space(after using raid 5, and converting 1gb = 1024 mb) it came down to about $1.33/GB. Really not that bad.

    As for some tips:

    -Cooling is very very important. Not really even with processor, but the drives. With four of them, they generate a lot of heat. Best thing to do is spread them as far apart as you can and install lots of fans to keep the air moving. Its also best to monitor the temp using the SMART tools in linux, at least for an initial testing period. If the drives are above 40C for a long time it will start eating away at their lifespan.

    -RAID will never be a substitute for a good backup plan. I almost found this out the hardware. I had a ATA bus, and a harddrive fail at the same time. Really screwed up the system. Luckly i was able to use the the linux's smart tools to remap the bad sectors on the disk, and then linux's raidtools to rebuild the drives superblocks. Long story short I saved all (most) of my data, that would of otherwise died on a raid system that i did not close control of. I am in the process of building a mirror for the raid server. You may or may not want to factor this in as a cost.

    -If your really serious about your data nothing beats a apple X-RAID(s) in a RAID 51 or 10 configuration. ;)

    if i can think of anything else i'll post it.
  7. csubear macrumors 6502a


    Aug 22, 2003
    One more thing that may help. You can buy metal brackets that let you mount 3.5" drives in 5.25" bays. With 5+ drives in a systems it helps. I've also seen people run SATA cables (via brackets on the back of the machine) to external drive enclosure that houses all of the drives).

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