Raid 0 with 4 HDD?

Discussion in 'Archived Threads 2001-2004' started by Mark Giles, Nov 13, 2002.

  1. Mark Giles

    Mark Giles Second Unit

    Joined:
    Aug 30, 2002
    Messages:
    272
    Likes Received:
    0
    Trophy Points:
    0
    My local CompUSA has a great deal on 30G HD. I was thinking about purchasing 4 and setting them up on raid 0. But when you set up 2 HDD on raid your supposed to use a seperate channel for each drive because of the disability of more than one instruction to be sent thru the IDE cable at once. If this is the case, wouldn't setting up 2 HDD on each cable have no advantage? How about using the new Serial cables on the new motherboards? Any difference?
     
  2. KyleS

    KyleS Screenwriter

    Joined:
    Jul 24, 2000
    Messages:
    1,232
    Likes Received:
    0
    Trophy Points:
    0
    The motherboards that support Raid usually come with 2 additional IDE channels onboard. So you have 2 masters and 2 slaves giving you a total of 4. You can also buy extra IDE PCI IDE cotrollers if your motherboard doesnt have the extra IDE controllers on board OR IF YOU NEED MORE to give you support for more the 4 drives. The instructions can be sent through the same cable at the same time but there is a finite amount of bandwidth for the drives to share.

    The new Serial ATA motherboards are available and on specifications alone would be the way to go BUT the Serial ATA drives are not readily available(If at all right now).

    KyleS
     
  3. John_Berger

    John_Berger Cinematographer

    Joined:
    Nov 1, 2001
    Messages:
    2,489
    Likes Received:
    0
    Trophy Points:
    0
    Um ... I have to ask ... why are you doing that?

    I find it extremely difficult to believe that the cost-effectiveness of using four 30 GB drives is better than a single 120 GB drive.

    You are (A) going to take up internal bay space and (B) going to get absolutely no redundancy benefits since one bad drive will destroy the stripe. You are also correct that two drives on a channel will not be good for a RAID 0 stripe. In fact, it will be hinderance. One benefit to RAID 0 is the ability to read from all spindles at the same time. Because you're dealing with IDE, two IDE calls will need to be made to read each block of data. In that case, a single drive would be far more efficient.

    I could understand wanting to go to RAID 5 or 0+1, but I'm curious as hell as to why you'd want to spend money on 4*30 RAID 0 when you'll get practically the same thing for 1*120 at a lower price.

    Or are the prices for the 30GB drives really that low?
     
  4. Steven K

    Steven K Supporting Actor

    Joined:
    Jan 10, 2000
    Messages:
    830
    Likes Received:
    0
    Trophy Points:
    0
    I have to agree with John... while it might seem that some benefit can be had from having two drives on a stripe (because you have two drives spinning, so you can get 'double' the speed) this just isnt the case, mainly due to the throughput limitations of IDE. SCSI, on the other hand...

    I would say that RAID 0 isn't even really true RAID but many people disagree... there's no redundancy, so if you lose one drive, you're hosed.
     
  5. Mark Giles

    Mark Giles Second Unit

    Joined:
    Aug 30, 2002
    Messages:
    272
    Likes Received:
    0
    Trophy Points:
    0
    John, This is a performance issue. I am not concerned with redundancy. Even with only 2 HDD, Strip 0 will negate redundancy. I know I am sacrificing fault tolerance for performance but I have a separate 60G HDD I use strictly for information that I do not want to loose and that I back up regularly. Since this is mostly a gaming PC, I find it very hard to use Raid 1 or (Raid 0+1 for that matter) given that half your HD space would be wasted when fault tolerance is of no concern. And are you saying that when using Raid 0 in both cases, a 1x120 drive will outperform 2x60 drives on two separate channels? Cost-wise, yes, of course you will end up paying more for multiple HDD but it will be far less money than say SCSI which has amazing performance specs. Again, my main goal here is performance. So if you agree that 2 HDD is better than 1 than is 4 better than 2 if you have only 2 channels available for Raid on your motherboard? The Raid manual to both of my motherboards state that Raid 0(Striping) requires 1 to 4 HD's. This is what prompted me to ask this.
     
  6. John_Berger

    John_Berger Cinematographer

    Joined:
    Nov 1, 2001
    Messages:
    2,489
    Likes Received:
    0
    Trophy Points:
    0
    But you're not getting performance - not with IDE. If anything, you're cutting performance because only two hard drives will be accessible at any one time (one drive on each IDE channel). A four disk stripe requires data to be read from all four disks since obviously the data is stripes across all four. In that case, since two can only be accessible at one time, a single read will require two disks to read then the other two disks to read. IDE does not allow four reads simultaneously across two channels.

    If you get one of the four-IDE channel motherboards, then you should be able to have four reads at once, but you'll need to make sure that there is only one disk per channel.

    The only way to truly get better performance from any kind of RAID setup in a PC or any kind of system is by going SCSI which does not suffer (as much) from channel interruption during device access. I can tell you right now that you're NOT going to get the same kind of prices with SCSI that you will with IDE.
     
  7. Wayne Bundrick

    Wayne Bundrick Cinematographer

    Joined:
    May 17, 1999
    Messages:
    2,358
    Likes Received:
    0
    Trophy Points:
    0
    There is some additional performance to be gained from having two drives on each cable (four total) vs. one drive on each cable. The maximum transfer rate may not go much higher but the minimum rate will. That's important for video editing.
     
  8. John_Berger

    John_Berger Cinematographer

    Joined:
    Nov 1, 2001
    Messages:
    2,489
    Likes Received:
    0
    Trophy Points:
    0
    No, because the IDE channel cannot address all four devices at one time. It can only address one device on a channel at a time. That means that to do a four-spindle read through two channels, the IDE controller will need to make two calls, one to the primary of both channels then one to the secondary of both channels, instead of a single call with one device on each of four controllers.

    Sorry, Mark, but I still see no advantage to this 4x30 configuration as opposed to a single ATA100 drive, separate from the boot drive, for data particularly since no redundancy or fault protection is involved. The data access restrictions of IDE are the problem here.
     
  9. Mark Giles

    Mark Giles Second Unit

    Joined:
    Aug 30, 2002
    Messages:
    272
    Likes Received:
    0
    Trophy Points:
    0
     
  10. Wayne Bundrick

    Wayne Bundrick Cinematographer

    Joined:
    May 17, 1999
    Messages:
    2,358
    Likes Received:
    0
    Trophy Points:
    0
    Sorry John, but in practice the IDE channel limitation is overcome by other factors. Four drives on four channels is indeed quite a bit faster than four drives on two channels because of the IDE channel limitation, but four drives on two channels is also faster than two drives on two channels. And all of the above are definitely faster than a single drive.

    Consider that the transfer rate of most drives will slow down as it seeks from start to end. Have you seen benchmark charts showing this? At the start of the test the drive is hauling ass but by the end of the test the transfer rate has slowed, perhaps as slow as half the starting rate. If you're capturing and editing video then you need a certain minimum speed from start to finish, or else you won't be able to use all of the disk capacity. Who wants to partition only the front half of a drive?

    Let's suppose a drive benchmarks at 40MB/s at the start and drops to 20MB/s at the end.

    An array using two of the same drive will benchmark at about 80MB/s at the start and about 40MB/s at the end.

    And an array using four drives may also benchmark at about 80MB/s at the start (due to the IDE channel limitation), but the transfer rate stays up around 80MB/s all the way to the end.
     
  11. John_Berger

    John_Berger Cinematographer

    Joined:
    Nov 1, 2001
    Messages:
    2,489
    Likes Received:
    0
    Trophy Points:
    0
    Maybe I've been hanging around Sun Microsystems sales peole for too long. [​IMG]
     
  12. Mark Giles

    Mark Giles Second Unit

    Joined:
    Aug 30, 2002
    Messages:
    272
    Likes Received:
    0
    Trophy Points:
    0
    Thx for the info Wayne...[​IMG]
     
  13. Kimmo Jaskari

    Kimmo Jaskari Screenwriter

    Joined:
    Feb 27, 2000
    Messages:
    1,528
    Likes Received:
    0
    Trophy Points:
    0
    You could always make sure you got a real speed boost and fork over for a 3ware Escalade raid card. They have up to 12 primary-only ide ports on those things.
     

Share This Page