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Rich Freeman wrote: |
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> On Mon, Mar 13, 2023 at 8:24 AM Dale <rdalek1967@×××××.com> wrote: |
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>> According to my google searches, PCIe x4 is faster |
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>> than PCIe x1. It's why some cards are PCIe x8 or x16. I think video |
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>> cards are usually x16. My question is, given the PCIe x4 card costs |
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>> more, is it that much faster than a PCIe x1? |
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> It could be slower than PCIe x1, because you didn't specify the version. |
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> |
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> PCIe uses lanes. Each lane provides a certain amount of bandwidth |
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> depending on the version in use. |
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> |
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> For example, a v1 4x card has 1 GB/s of bandwidth. A v4 1x card has |
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> 2GB/s of bandwidth. |
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> |
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> Note that slot size is only loosely coupled with the number of lanes. |
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> Lots of motherboards have a second 16x slot that only provides 4-8 |
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> lanes to save on the cost of a PCIe swich. You can also use adapters |
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> to connect a 16x card to a 1x slot, or you might find a motherboard |
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> that has an open-ended slot so that you can just fit a 16x card onto |
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> the 1x slot. It will of course only use a single lane that way. |
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> |
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> So what you need to do is consider the following: |
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> |
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> 1. How much bandwidth do you actually need? If you're using spinning |
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> disks you aren't going to sustain more than 200MB/s to a single drive, |
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> and the odds of having 10 drives using all that bandwidth are pretty |
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> low. If you're using SSDs then you're more likely to max them out |
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> since the seek cost is much lower. |
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> 2. What PCIe version does your motherboard support? Sticking a v4 |
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> card on an old motherboard that only supports v2 is going to result in |
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> it running at v2 speeds, so don't pay a premium for something you |
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> won't use. Likewise, if they cut down on the number of lanes assuming |
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> they'll have more bandwidth you might have less than you expected to |
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> have. |
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> |
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> Then look up the number of lanes and the PCIe version and see what you |
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> can expect: |
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> https://en.wikipedia.org/wiki/PCI_Express#History_and_revisions |
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> |
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> I think odds are you aren't going to want to pay a premium if you're |
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> just using spinning disks. If you actually wanted solid state storage |
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> then I'd also be avoiding SATA and trying to use NVMe, though doing |
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> that at scale requires a lot of IO, and that will cost you quite a |
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> bit. There is a reason your motherboard has mostly 1x slots - PCIe |
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> lanes are expensive to support. On most consumer motherboards they're |
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> only handled by the CPU, and consumer CPUs are very limited in how |
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> many they offer. Higher end motherboards may have a switch and offer |
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> more lanes, but they'll still bottleneck if they're all maxed out |
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> getting into the CPU. If you buy a server CPU for several thousand |
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> dollars one of the main features they offer is a LOT more PCIe lanes, |
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> so you can load up on NVMes and have them running at v4-5. (Typical |
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> NVMe uses a 4x M.2 slot, and of course you can have 16x cards offering |
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> multiples of those.) |
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> |
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> The whole setup is pretty analogous to networking. If you have a |
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> computer with 4 network ports you can bond them together and run them |
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> to a switch that supports this with 4 cables, and get 4x the |
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> bandwidth. However, you can also get a single connection to run at |
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> higher speeds (1Gb, 2.5Gb, 10Gb, etc), and you can do both. PCIe |
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> lanes are just like bonded network cables - they are just pairs of |
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> signal wires that use differential signaling, just like twisted pairs |
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> in an ethernet cable. Longer slots just add more of them. Everything |
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> is packet switched, so if there are more lanes it just spreads the |
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> packets across them. Higher versions mean higher speeds in each lane. |
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> |
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|
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|
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This is why I asked. I didn't even think about the different PCIe |
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versions available. My mobo, had to go dig out the manual, says it is |
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PCIe 2.0. This is a Gigabyte 970A-UD3P motherboard. Yes, I'm thinking |
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about building a new rig. Turn this into a NAS maybe. Anyway, I'm |
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assuming 2.0 isn't the slowest or fastest but as you point out, it'll be |
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a bottleneck. Everything has a bottleneck somewhere. |
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|
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The difference in price isn't that large. What I did was, I saw the |
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PCIe x1 and bought it. It supported Linux. Later on I noticed the PCIe |
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x4 and then wondered if I should upgrade to that. Given the limits of |
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my mobo and the fact I won't be maxing out the drives anyway, I don't |
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see the need to upgrade. Your info pretty much makes that clear. I |
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might, just might, see a small difference when using pvmove. Maybe. |
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Given that it generally maxes out the drive as it is, even if it does go |
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faster, it won't be much. Add in that when I start a pvmove, I go nap |
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and do other things anyway, I won't notice it. Last pvmove took a |
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little over 19 hours. Even 20 or 30 minutes isn't much difference in |
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the grand scheme of things. |
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|
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Another question. My rig is getting a bit aged. I have a AMD FX-8350 8 |
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core CPU running at 4GHz. I also have 32GBs of memory. I've read that |
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Intel currently has the best bang for buck on CPUs nowadays. I'm open |
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to the idea of switching. As far as speed goes, if I built a new rig |
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that is using a reasonably cost CPU and memory, would I see any real |
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improvements? When I say 'reasonably cost', I usually find the |
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fastest/newest then drop down a bit to get out of that 'brand new' price |
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point. Generally, the difference in price is quite large but the |
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difference in speed isn't that much. Also, I got hard drives, I don't |
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spend much on video cards either since I don't game, except solitaire. |
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So, let's say a mobo, CPU and memory. What price range would I need to |
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look for? Just a rough idea. I figure the CPU will be a few hundred. |
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Memory may be half that. Mobo will likely be close to $200 or so. I'm |
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thinking $500 to $700 or so. Then comes case, video card and all that. |
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The CPU, memory and mobo is the ones I try to buy all at once from the |
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same vendor, like Newegg or Tigerdirect. Thoughts? Am I close? |
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|
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Thanks for the info. At least I know I'm good on drive speed. For my |
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use anyway. |
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|
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Dale |
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|
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:-) :-) |