RAID levels - performance (revisited)

Discussion in 'OT Technology' started by dissonance, Nov 27, 2007.

  1. dissonance

    dissonance reset OT Supporter

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    I don't mean to start the discussion again, I just ran across this comparison while doing some research at work and thought I would share.

    http://dissonance.us/fusionowners/up/raid_performance.zip

    (I'm at work so I just used my uploader to host it. It is a pdf file but apparently I forgot to have the uploader allow .pdf files so its been zipped)
     
  2. deusexaethera

    deusexaethera OT Supporter

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    I have a good link at work. I'll post it when I get in in the morning.

    All most people need to know is that:

    1. Use RAID1 if you can only afford two disks, or if you don't have room for 3+ disks;
    2. Use RAID5 if you can afford 3+ disks;
    3. Use RAID3 if you're going to be doing a lot more reading than writing (movie/music servers and the like), assuming you have the option to use RAID3.
    4. RAID0 should be avoided under all normal circumstances.

    There are other RAIDs like RAID10, RAID01, and RAID50, but they all cost a shit-ton of money. There are exotic RAIDs too, like RAID4, RAID6, and RAID7, but they're only useful in very specific circumstances, so they're not worth Joe User's time and money.
     
    Last edited: Nov 28, 2007
  3. ParTyBoy

    ParTyBoy New Member

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    I would contend that RAID6 is very useful with larger than 2TB arrays. Today's 3.5" magnetic disk hard drives are increasing in capacity by leaps and bounds, yet physical speed is not increasing at the same pace.

    This leads to a particular issue when using RAID5 with large arrays. RAID5 allows for single fault tolerance. If a second drive fails, you lose all data.
    The larger the array, the longer it takes to rebuild. It is entirely possible that a second drive could fail while rebuilding an array.

    RAID6 had dual fault tolerance. Two drives can fail and the information is still intact. This is why it is an optimal choice for larger arrays.
     
  4. deusexaethera

    deusexaethera OT Supporter

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    Learn to read, sparky. Anybody who needs 2TB of data on-tap at all times is, by definition, not Joe User.

    Also, among the hardware I manage is a $40000 IBM SAN configured as four spanned RAID5's, each with one parity drive and one hotspare. It has never failed. Maybe it would have problems if it were operating while bouncing around in the back of a mobile datacenter (i.e. an 18-wheeler), but that's the only time it would have problems.
     
  5. ParTyBoy

    ParTyBoy New Member

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    I read your post accurately, and I think that years ago with smaller drives it would have been appropriate to consider RAID6 a luxury, not a necessity. Seeing as you consider yourself an IT professional you should be aware that drives with similar build dates and/or equivalent uptime are prone to failure within short time of initial hardware failure. As stated, RAID5 is not optimally suited to keep data safe when you start dealing with large capacity drives and longer rebuild times.

    However, suggesting that RAID6 is useful under very specific circumstances is ignoring the fact that consumers now have the ability to purchase drives in the following sizes at reasonable prices.

    500gb - under $100
    640gb - 2 platter samsung should be under $140
    650gb - $109.99 frys
    750gb - under $180
    1TB - under $300

    Samsung has already announced a 1.5TB drive for Q4 2008. PMR is raising magnetic density and in turn this is boosting sustained write speeds, but this is still minor compared to the increases in capacity. Maybe you should re-examine your opinion of RAID6 given the limitation of RAID5 single fault tolerance.
     
    Last edited: Nov 28, 2007
  6. deusexaethera

    deusexaethera OT Supporter

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    Joe User isn't going to spend $400 (4x 500GB), plus the cost of a specialized RAID6 controller, to store his porn with twice the safety offered by RAID5. Drives don't fail that often; yes, it's possible that two drives could fail back-to-back, but whereas an array has a 100% chance of dropping 1 drive in its lifetime, it has a ridiculously small chance of dropping two drives within a couple hours of each other.
     
  7. ParTyBoy

    ParTyBoy New Member

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    That depends on your interpretation of Joe user.

    Joe user 3 years ago couldn't purchase 2TB for a reasonable price. That's not the case anymore. The RAID6 card is obviously the most cost prohibitive component seeing as you're pretty much limited to Areca cards, 3ware 9650, or an Intel card.

    You can occasionally find a used card for a good price though. Even so I do believe that you underestimate the notion that as high capacity storage becomes more affordable, home users are more inclined to expand home storage to meet their needs.

    Cheap, high power output enthusiast power supplies are also helping this along. Sure it's not a dedicated UPS, but it doesn't have to be for a home server.
     
  8. deusexaethera

    deusexaethera OT Supporter

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    My interpretation of Joe User is based on the various people whose home PCs I've seen. Even the computer-savvy friends I know have no need for a 2TB storage array, and none of them would consider $1200 + RAID6 card to be a reasonable price at this point. Maybe if they had that much data they would think so, but at the same time I doubt any of them would be inclined to spend more than $500.
     
  9. dissonance

    dissonance reset OT Supporter

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    Hey, I would consider myself a Joe user and I just spent >$400 on 5 320gig Seagate ES drives for my RAID5... and I have a $750 controller. Now granted I got the controller for free.... :naughty:

    maybe that makes me not a Joe user after all. And I would possibly do a RAID6 if I had the room for 2 hot spares
     
  10. 5Gen_Prelude

    5Gen_Prelude There might not be an "I" in the word "Team", but

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    Joe user doesn't even know what RAID stands for or what it can do.
     
  11. StevesVR4

    StevesVR4 Get Arrested

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    A better option for Joe User than RAID6 is RAID5 with a hot spare. The cost of the controller is much lower than RAID6 controllers and you have an extra drive available for the case where one drive fails. The controller should automatically rebuild on the spare drive without the users intervention. The chances of a second drive failing before the array rebuilds is statically insignificant. For a mission critical application where even the remote chance of two drives failing cannot be risked, sure RAID6 is needed. For the home user, the added cost is not worth it.
     
  12. dissonance

    dissonance reset OT Supporter

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    I would have to agree with this. I offered an extra RAID controller to someone I know who has ~1.2TB of used storage (mostly spread upon external hard drives). My idea was that she would move those drives inside the case and use the card. Needless to say, someone (her) who I was sure would have really wanted the card didn't have a clue what it was.
     
  13. ParTyBoy

    ParTyBoy New Member

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    I'll concede, that a majority of home users will not justify such an expenditure, nor are 70%+ of home users tech savy enough to implement and maintain a RAID. (assuming the rest should have enough patience to accomplish such a task)

    The number that can justify an expenditure will only increase as high capacity drives continue to drop in price. (although most probably will still not realize the need for RAID redundancy :hs:)

    Another change that will help foster the use of controller cards in home environments is the general transition from PCI-X to PCI-E interface. You used to have to purchase a potentially costly server board with ECC registered ram to have PCI-X at home, or use a compatible PCI-X card in a home motherboard PCI slot while running in a reduced state.

    Motherboards aimed at home users with 2-4 PCI-E 16x slots are becoming fairly prevalent now, which is also making it easier to eliminate the need of a dedicated server system.


    BTW: you could do 2TB RAID6 for under $1000 if you try hard enough. The tough part is finding and obtaining an 8 port card.
     
  14. deusexaethera

    deusexaethera OT Supporter

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    I don't think so. The trend of simply buying larger single drives as they drop in price has held fast so far, and for good reason; it's simple, it's cheap, and it doesn't require any brainpower. I think it will continue to be the norm.

    Besides, the cost of the drives is rarely the cost-prohibitive factor in any RAID; at work our workstations have 4-disk SCSI RAID5's, and while the drives cost $250 apiece, the controller (LSI MegaRAID) costs $1200 just by itself. Those controllers are a mature technology at this point, and any advancement is only incremental to keep up with the speed of the disks themselves, so their cost isn't going to change substantially. Even a comparable SATA RAID card is only a couple hundred bucks cheaper, whereas comparable SATA drives are a quarter of the price if not even less.

    The only RAID that I think will ever be within easy reach for home users is RAID1, because it doesn't require special XOR hardware. That's why even cheap Dells have RAID1 support now. But hey, RAID1 is just as safe as RAID5, so I say anybody who wants one should get one -- if it saves you a single day of restoring backups, it's paid for itself.

    You don't need PCI-X to run a RAID with an offboard card. I have an offboard PCI card running my RAID (NetCell), and even with the PCI bottleneck my thoughput jumped 76% compared to a single disk running on the onboard SATA controller.

    Well shit man, hook us up with some links. I know there are people here who'd drop the money on it just for the novelty.

    - - -

    EDIT: For further comparison, that $40000 SAN I have at work has 33 Fibre Channel drives in it, each costing $300. That means, of the $40000 price tag, only $10000 goes towards the hard drives -- the enclosures, the backplanes, the backup batteries, and the redundant controllers represent a full 75% of the cost of the unit. So even in RAIDs with large numbers of drives, the drives aren't the cost-prohibitive factor.
     
    Last edited: Nov 29, 2007
  15. ParTyBoy

    ParTyBoy New Member

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    You can find deals for used controller cards on Ebay. Most of these cards are pulled from operating servers and have passive heatsinks. They're usually a safe bet. If this is not an acceptaible risk then there's Newegg (but you're going to pay more)

    I've seen 8 port Areca cards go for under $300. There's a 3ware 9650se 8 port on eBay now at $222 with 3 days to go.

    As far as hard drives, wait for deals to pop up on fatwallet or slickdeals. There are 500gb drives that have sold new for as low as $80. Frys.com had a deal last Friday-this monday on 750gb internal Seagate drives for $160
     
    Last edited: Nov 29, 2007
  16. ParTyBoy

    ParTyBoy New Member

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    It seems Highpoint is finally deciding to use dedicated XOR processors

    Highpoint 3520ML uses the same Intel IOP341 processor as Areca's latest generation of cards. The card has a PCI-E interface, allows for 8 sata drives and is capable of RAID6. Unfortunately, Highpoint only is offering one product based on the IOP341 at this time, no 12, 16, or 24 port card is available.

    http://www.highpoint-tech.com/USA/rr3520.htm

    The Highpoint 3520 is approximately $80 less ($432 apx) than the Areca 1220 and 3ware 9650SE-8LPML ($510 apx).


    Highpoint's PR test comparison (be aware that Areca 1220 uses the older Intel IOP333)

    http://www.highpoint-tech.com/USA/rr3520_Performance.htm




    .
     
    Last edited: Nov 29, 2007
  17. StevesVR4

    StevesVR4 Get Arrested

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    For home users, the lack of a dedicated XOR processor is not as significant today with the prevalence of dual and quad core processors. It is not like the last year or two when practically every new home computer had one processor with one core that would have needed to split time between XOR processing and the application that is running. Now that computers are coming with two and four cores, the XOR processing can run in parallel with the application and XOR processing occurring on separate cores. RAID5 is now in reach of the home user without using a dedicated RAID card. The Intel ICH9R supports RAID5 and you can pair it up with a Core 2 Quad processor for what should be fairly decent speed.
     
  18. ParTyBoy

    ParTyBoy New Member

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    What happens when the user decides to upgrade their computer and swaps out their motherboard? :o
     
  19. deusexaethera

    deusexaethera OT Supporter

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    The man's a thinker.

    With RAID1, though, it won't matter.
     
  20. Peyomp

    Peyomp New Member

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    For Joe User - ZFS is where its at. They can't have it yet, but they will. You'll see this being used in upscale media centers in the next few years.
     
  21. deusexaethera

    deusexaethera OT Supporter

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    Just as soon as it's not part of *nix anymore, yes.
     
  22. Peyomp

    Peyomp New Member

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    Windows is very, very weak in this space. Embedded systems like... Tivo are using Linux. People don't want Windows on their TV. *nux has a larger share of this market than windows ;)
     
  23. StevesVR4

    StevesVR4 Get Arrested

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    What happens when the RAID card goes belly up and needs to be replaced? :hsugh:
     
  24. deusexaethera

    deusexaethera OT Supporter

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    You replace it.
     
  25. ParTyBoy

    ParTyBoy New Member

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    As deusexaethera stated, you replace it. You either replace it with the same manufacturer/model of card, or you may be able to replace it with a newer model from the same manufacturer. You need to check with the manufacturer of the card.

    This is a better scenario, than being forced to use the same motherboard, because your raid is dependent on the motherboard RAID controller.
     

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