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  1. #1
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    Question Software RAID CPU load?

    So I just got a server for about $100 and found out the provider don't offer hardware RAID so I am thinking of using software RAID. I will be using it to host my own sites, which is about 1GB in size, most of it from the MySQL databases. Considering the RAID would only be working on about 1GB of data, is the software RAID going to use a lot of CPU?

  2. #2
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    No it won't use too many cpu resources. For this little data you shouldn't even notice it.
    What kind of server config do you get?
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  3. #3
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    Core2Quad Q9550
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  4. #4
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    Is it normal for provider to charge a monthly fee for software RAID? I thought that software RAID is built into the Linux kernel and costs nothing additional?

  5. #5
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    Quote Originally Posted by chasebug View Post
    Is it normal for provider to charge a monthly fee for software RAID? I thought that software RAID is built into the Linux kernel and costs nothing additional?
    I don't see why they would charge, but each provider is different.

    You shouldn't see much of a speed difference/cpu usage. The CPUs these days are powerful enough for that.

    The pros outweigh the cons, though.
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  6. #6
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    Yes, so I guess it depends on the provider. It just seems like nickel and diming to me. Or maybe for that $10 they will setup the software RAID and rebuild the RAID array if a hard drive fails, that would be acceptable IMO. But that should really be a one-time fee not monthly anyway.

  7. #7
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    Quote Originally Posted by chasebug View Post
    Yes, so I guess it depends on the provider. It just seems like nickel and diming to me. Or maybe for that $10 they will setup the software RAID and rebuild the RAID array if a hard drive fails, that would be acceptable IMO. But that should really be a one-time fee not monthly anyway.
    Generally speaking, software RAID requires a hand install unless you want stock partitioning in a RAID1 etc.

    I don't know why they'd charge a monthly fee, though.
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  8. #8
    Software RAID is free in most companies but some others charge you for it. And the price is less than $20/month as i know in most cases. And with your server specs, you can ask your provider to do it for you. Maybe they do offer it for free to you too.

  9. #9
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    It actually depends on the type of RAID you use.

    RAID 0, 1, and 10 use very little CPU resources (1-2%).

    RAID 5 and 6 would consume a LOT of CPU resources (10-50%).

  10. #10
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    I have heard some horror stories when sync'ing data if one of the disk failed. If you can afford, try to get hardware raid.

  11. #11
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    The raid itself might not use a lot of cpu, but it'll be noticeable if you ever have to rebuild a disk. Linux SW raid for root disks is not terribly good, so if you can get a HW raid controller its probably worth it.
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  12. #12
    Quote Originally Posted by brentpresley View Post
    It actually depends on the type of RAID you use.

    RAID 0, 1, and 10 use very little CPU resources (1-2%).

    RAID 5 and 6 would consume a LOT of CPU resources (10-50%).
    I would disagree here. Although the common perception is that raid 5 software is really heavy on cpu use, I really only saw a few percent use while copying a large amount of data from a single drive into a raid 5 array. Maybe 5% of one cpu core. The performance itself wasn't fantastic, but it certainly wasn't cpu limited, or even having a large impact on the cpu available in general.

    Hardware raid cards with powerful processors and battery backed cache memory are going to be higher performance for raid 5 than software raid will be, but the cpu savings are hardly much to get excited about. For raid 1 / 10, there's really no difference at all.
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  13. #13
    Quote Originally Posted by gate2vn View Post
    I have heard some horror stories when sync'ing data if one of the disk failed. If you can afford, try to get hardware raid.
    I have similar horror stories with hardware raid, so I won't touch them if I can help it. Whenever you're dealing with your critical data, one or two bad experiences will easily make you prefer one solution over the other, but done properly, hardware or software would be a good choice.
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  14. #14
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    Quote Originally Posted by funkywizard View Post
    Hardware raid cards with powerful processors and battery backed cache memory are going to be higher performance for raid 5 than software raid will be, but the cpu savings are hardly much to get excited about.
    It is quite exciting when you think about the offloading of consistency checking and rebuilding. If you've ever watched a multi-terabyte raid array rebuild, you'll be glad its not your system CPU doing it.
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  15. #15
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    Quote Originally Posted by funkywizard View Post
    I have similar horror stories with hardware raid, so I won't touch them if I can help it.
    I've seen a variety of raid failures in my career, but I've seen the most failures in ext2/3 failing rather than the raid itself. In terms of the number of HW vs SW failures, I've seen at least 2x more failures with SW raid due to improperly supporting the underlying hardware. If you're using a HW controller, it interacts properly (usually) with the hardware and insulates the OS from the physical problems.

    If you've ever watched a machine get stuck while trying to poll a dead channel, you know what I'm talking about
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  16. #16
    Quote Originally Posted by appliedops View Post
    It is quite exciting when you think about the offloading of consistency checking and rebuilding. If you've ever watched a multi-terabyte raid array rebuild, you'll be glad its not your system CPU doing it.
    A valid point, but at the same time, you want to make sure that the raid card is sufficiently powerful enough as well. Just any-ol' hardware raid card is not going to be better than software raid, and can be substantially worse if you're not careful. You have to do your homework to figure out which cards have a powerful enough cpu to actually be doing more good than harm with parity calculation speeds. For the kind of money it costs to get a really good card, I don't see a lot of point to it in most usage scenarios. Of course there are some times when a really good raid card is well worth the money, but I don't come across that very often.
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  17. #17
    Quote Originally Posted by funkywizard View Post
    I have similar horror stories with hardware raid, so I won't touch them if I can help it.
    ^^ This I was going to say, but I thought I'd let somebody else do it. Things break this is why we do backups.

    RAID is one of those things that will help you in a bunch of situations to save time, but it isn't the be all and end all of data security if you have a hw controller or using sw raid. Sometimes a whole slew of drives fail at the same time or your controller will catch fire. Hardware v software raid is about removing some load to a seperate device that doesn't interfere with the load of your system - also seperate cache and BBU et al is nice.

    One of the ways you can break both is by not understanding what you're working with an totally misconfiguring them - which is granted easier to do with sw raid but it's still solid code in linux.

    If you need those things go for it, if you don't then it's optional..

    I've tested SW raid 0, 1 and 10 on Linux at ram disk speeds and haven't seen much in the way of noticable CPU load. Yeah when syncing it can but you're loading the crap out of disks at this point so you're not going to see much in the way of performance be it from a hardware controller or sw raid.

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