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software raid in G5

Discussion in 'General Mac Discussion' started by adamfilip, Jul 21, 2003.

  1. macrumors 6502a


    im wondering

    how well does the software Raid setup work?

    im thinking of getting dual 36gig WD raptor hard drives for my new 1.6ghz g5..

  2. macrumors 6502

    I was wondering the same thing. But I don't think it's possible to boot from a software raid.
    So you'll need to have a seperate partition to boot from..
    Does anyone here know more about this?

    ( I know that the software raid from OS X works really well. You can raid anything you want. There was this guy who made a software raid out of 5 usb floppy drives :D )
  3. macrumors 68040



    I don't wish to second-guess you, but for what purpose do you wish to RAID these drives? And to what level?

    I only ask as RAID 0's only real purpose is to make a computer think that many physical partitions are one logical partition, but there is no redundancy, no "R" in the "RAID" at that level ergo, not really RAID.

    If you wish to RAID for video, it would be best to have a lot more drives, and go to RAID 3 at least.
  4. macrumors 65816

    Software raid works well, and is bootable. I've got two disks in raid-0 as the only disks in my machine.
  5. macrumors 6502

    I was thinking RAID 0. I would like to do RAID 5 but you can only put 2 HDs in the G5.
    I agree with you that RAID 0 is not very redundant, so AID would be the best name.. But imagine a RAID 5 using say 6 15k SCSI disks, not really Inexpensive either ;)

    Nice to hear that it's possible to boot from software raid!


    My goal is video editing indeed & large photoshop files. I like my performance to be high, and RAID 0 is better than no RAID. Yes of course it best to use 10 disks in a RAID 50 setup, but there is this money issue. :D
    I'm still looking at the options. I'm not sure whether I'll use RAID. RAID 0 is not very secure, and I've had a HD crash before..
    I think I'll start with the 10k rpm WD Raptor.


    RAID 0 is striping, you'll get much better performance than with one disk alone. Especially with the serial ATA and it's independent busses.


    More info on RAID 0
  6. macrumors 6502a


    is there any site that has benchmark results.. in regards to apples software raid.. setup?
  7. macrumors 6502

    I looked for some specific info on how OS X stores the RAID configuration info but didn't find anything in ~5 minutes of searching so I'm just going to throw out some general software RAID info.

    Software RAIDs can be "tricky" depending on how the system sets them up. NT4 stores its software RAID info in the registry. If the boot drive dies, so does the info needed to access the software RAID. You're stuck calling a data recovery service and paying $$$ to get your data back. Sure, you can save the data in a safe place and manually plug it back into the registry of a fresh OS installation but you need to know what to save and where to stick it in the new system.

    Before using a software RAID, learn how your system stores the RAID configuration info and learn how to recover your RAID from a catastrophic system failure. Better yet, get a hardware RAID controller. They're independant of the OS and crash-proof. Sure, lightning will still damage your system beyond repair but the RAID is completely isolated from the system and appears to be a single large drive to the OS and you don't have to worry about saving the configuration info or remembering how to get the RAID mounted on a fresh system installation. It also takes the processing burden off the CPU.

    Just my $0.02.
  8. macrumors 65816

    If you are worried about data safety with raid-0 get a firewire disk or another machine and rsync your important directories via cron. I do that between my Linux machine with raid-1 and my Mac with raid-0, keeps three copies of the data.
  9. macrumors 65816


    There are no stupid questions -- just stupid people asking questions...

    If I have two drives, each with two partitions, will OS X's software RAID let me use RAID 1 on one pair (across two disks) and RAID 0 across the other two?
  10. macrumors 68020


    Software-base RAID 5 is absolutely the last thing you would want to do for a video application. You'd spend all your CPU time recalculating the parity as you write out your video stream. RAID 5 is never the right choice for write intensive i/o patterns. For read-mostly applications, RAID 5 is OK, but with the price of drives these days, I always recommend RAID 1+0 (mirrored and striped) for high performance *and* reliability. Most commercial RAID 5 implementations use special hardware in the RAID controller to do the parity calculations. Even then, it's not the best choice in write intensive workloads.

    Just my experience.
  11. macrumors 6502

    Thanks DaveL for the info.

    I found 2 reviews of the WD360 Raptor:


    Extremetech is less happy about the Raptor.
  12. macrumors 68020



    I'm surprised the Raptor isn't more dense. At 36 GB, it's one of the least dense drives currently on the market. The Maxtor Atlas 10k is 4x as dense and in the same (actually a bit higher) performance class, although the price is up there, as well.

    The other plus for the Raptor, for me, was the lower operating temperature.

    So, are you going to get the smallest single drive in the G5 and then replace it with 2 really fast ones (10K RPM)? If you are going to stripe, you really want to use drives that match.
  13. macrumors regular

    They could both have the same density. The Maxtor may just have more platters inside it. I *think* I remember reading that the raptor is a 1 platter drive. I'd setup a RAID 0 as a scratch disk, nice and fast and since you aren't permenanty storing information there, you don't really have to worry about reliability. Then again the G5 only has 2 hard drive bays. Two steps forward, one step back.....
  14. macrumors 68040



    Well, that's due to the combination cost factor/space factor/cooling factor/ and the fact that FW 800 abrogates the need.

    Usually if a person wants more that what two drive can provide, it's a pro who'll use a hardware RAID array anyway.
  15. macrumors 6502a


    i was thinking. of getting two raptors.. internal and then turn the existing drive into an external if possible or just buy a large 250gig drive.. for backup..
  16. macrumors 68020


    Sure, just take the original internal out and buy a external firewire enclosure for it. OWC has FW400 enclosures for about US$90. FW800 enclosures are more expensive; I wouldn't bother for a single drive.
  17. macrumors 65816


    Can someone explain RAID in layman's terms for a sec?
  18. macrumors 68040



    RAID is an acronym for Redundant Array of Independant Drives. And as the name suggests, it requires more than one hard drive, and prefers all the drives to be the same size.

    The most obvious effect of a RAID'ed set of drives is that, to the computer, they look and therefore act like one hard drive, instead of several.

    There are levels of RAID, each doing different things. Level zero (0), is also called "striping", and all it does is make the drive look like one.

    However, when you get up to level 3 or higher, the drives actually begin to parse the datas you are saving to them into pieces and distribute the pieces evenly across some of the drives - and others in the array back up (Redundant) the first set. This way when one of the drives fail, you don't lose anything.
  19. macrumors 603


    i would disagree with you on that, RAID 0 allows you to have two sets of read/write heads rather than one, so with the data striped across both drives, both disks can be seeking/writing info at the same time... There is a performance boost (in disk-intensive uses). It's intention is just that, not making two drives appear as one.

  20. macrumors regular

    JBOD or Just a Bunch Of Disks is a RAID "like" method for making more than one drive appear as one.
  21. macrumors 68040



    You are correct, and that is a natural benefit to having two (or more) drives as one. But he wanted layman's terms. :D

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