Questions about setting up a RAID

Discussion in 'OT Technology' started by kiLLj0y, Nov 27, 2004.

  1. kiLLj0y

    kiLLj0y New Member

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    I just bought my second 200gb hard drive, and am thinking of setting up a RAID. They are going to be used soley as storage space for downloaded junk. My operating system and installed programs are on a seperate hard drive. As I have the funds in the future, I hope to add another 2 drives as well. [​IMG]

    My first question would be is RAID 0 worth it? I read something claiming that it REDUCES the reliability of the hard drives. I know in the future I would like to move to a RAID 3, I belive it is, with 1 drive being for parity, which would help reduce my worries of reliability.

    Also, when I set up the RAID, will both drives need to be empty? My current 200gb hard drive has a ton of junk on it. Would I need to format it and start with 2 blank hard drives? Would I be able to move from RAID 0 to RAID 3 without starting fresh again?
     
  2. P07r0457

    P07r0457 New Member

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    RAID 0 is horrible. Speed increases are negligable... seriously nothing improved. Furthermore, your MTBF is halved... Meaning that your chance of failure doubles. And if that wasn't bad enough, simply losing power, or having a blue-screen lock your system up could cause the array to be in an inconsistant state -- ruining all the data on your system.

    I would *never* run RAID0.

    RAID3 is also rather pointless. The common forms of RAID are 0, 1, 5, and 0+1. I hope you do not consider 0. 1 is the most secure, but is the most costly in terms of space (N/2 where N is the number of drives, minimum 2). 5 is extremely secure, and good with space due to it's parity (N-1 where N is the number of drives, minimum 3). 0+1 uses a combination of techniques to stripe two drives and mirror the stripe (N/2 where N is the number of drives, minimum 4).

    Typically, you must format when moving between RAID levels... Especially when going from a basic setup (0, 1, 0+1) to something that utilizes a parity. Intel's newest RAID setup featured on their high-end 925 motherboard allows you to move without data loss. Some other options exist.

    Overall, you are much better using either JBOD (if you want to easily add drives w/o losing anything) or simply mounting them as seperate drives.

    If you wish to use a parity setup, then do that from the start -- and you must start with the total number of drives. Additional drives cannot be added later, except as hot-spares, which do not increase usable space.
     
  3. kiLLj0y

    kiLLj0y New Member

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    Looks like I will be mounting them seperately, which sucks for my FTP setup. :hs: JBOD doesn't seem to have any real positive to it, other than the disks appearing as one. Some site claims no performance gain is to be had, and it still requires a controller.

    Maybe one day I will buy a few more drives and setup the RAID 5. :coold:
     
  4. P07r0457

    P07r0457 New Member

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    JBOD does not require a controller... windows xp pro and server can do this natively w/o a controller.
     
  5. kiLLj0y

    kiLLj0y New Member

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    Where in XP Pro can I find some information about this? :)
     
  6. Mikey D

    Mikey D New Member

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    Software raid sucks, pointless.
     
  7. Penetration

    Penetration OT Supporter

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    for larger files and loading games there is quite a noticable difference in speed. though there is more risk of disk failure, it's a risk I'll take.
     
  8. P07r0457

    P07r0457 New Member

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    data that's worth risking probly isn't worth having anyway.
     
  9. crontab

    crontab (uid = 0)

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    Depends on the data you put on that particular volume(s). I have a few stripes sets at home they only contain games, mp3's, movies, porn, crap I do not care about. We have stripe sets set up at work for our test and benchmark environments for PTG testing or development. Again, the data on there is insignificant or not required to be highly available, where data can be restored from tape. Raid 0 doesn't reduce reliability of the drives, it increases probability of data loss, big difference. A few things to note, I've broken and lost many stripe sets due to user and/or hardware/software "controller" errors. But recovered to a working state 99.9% of the time w/o restore just by rebuilding the stripe set with the meta data on the members. Easily done with enterprise level hardware/software raid controllers, but I did this with the crappy home pc controllers as well. But if you lose a drive, you lose your data, period. Bear in mind hard disk errors, like blocks dieing on a platter will behave the same in any raid set when compared to a single disk/jbod. Also note that parity raid sets are slightly slower since it will take some cycles for the controller/cpu to calculate the parity.

    Most home based scsi/ide/sata pseudo-hardware controllers do not let you perform this task, you must completely wipe out everthing on the disk in order to build your new raid sets. I don't believe windows 2k+ software raid lets you do this as well. But packages like Veritas Foundation Suite or HP LSM lets you migrate from different raid levels and add/subtract members on/from the raid set on the fly without loss of data. Some hardware controllers with vraid let you do this as well.

    So, if you don't care if you lose your data go raid 0, else don't even plan on doing it. Unless you backup religiously. Good Luck.
     
  10. crontab

    crontab (uid = 0)

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    Almost all raid setups for HOME usage are software even when you have something onboard like the promise or highpoint raid controllers. You need drivers (software) to see the actual raid sets being presented from the so-called onboard raid controllers. A real hardware controller presents that lun as a volume and the OS doesn't need a driver to see that volume, only the driver for the HBA, host bus adapter to see the luns regardless if they are striped, mirrored, parity, or just a bunch of disks.

    There are benefits to software raid that hardware raid can not perform. Like distance in members. Say you want to build a 0+1 raid set and want to utilize even more high availibility by keeping the stripe sets in different data centers or labs or circuit grids that are more than 500 ft away. Some hardware controllers need the disks to be about 100 feet away, even arrays over glass or fiber. Software raid can accomplish this task just fine with the properly built fabric with mesh/switches/trancievers/hba's. But there are new expensive hardware products coming out to help accomplish this task.

    But there are advantages to hardware raid as well. Just depends on the environment.
     
  11. Mikey D

    Mikey D New Member

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    I figured you'd chime in on this thread.
     
  12. P07r0457

    P07r0457 New Member

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    :bsflag:

    the need of a driver in windows does *not* make it a hardware or software solution. Agreed that onboard controllers and many cheap pci controllers are software-based -- however there are many hardware controllers that still require drivers! Even high-end SCSI cards require drivers... However, in some cases, microsoft has these bundled already with the OS. Regardless, that is not an indication of whether it's a hardware or software implementation.
     

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