Pls Calculate MB/s - 2x mirror SSDs on x4 PCIe

Discussion in 'Mac Pro' started by gr8putt, Feb 19, 2018.

  1. gr8putt macrumors newbie

    gr8putt

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    #1
    I've a 5,1 Mac Pro (2010, 3.33 12-core) and a big fat AMD Radeon R9 280X in lowest PCIe x16 (don't think anything will fit in the x16 slot above).

    I'm hoping to put two OWC Accelsior S PCIe SSD Addapter cards (mirrored) in the two free x4 PCIe slots -
    "Accelsior S is the simple solution to add a high speed SATA 6G drive to PCs or silver Mac Pro towers otherwise restricted to 3G architecture."

    MacSales Tech checked and confirmed two mirrored Acc/S adapters would work but preferred the x16 slots.

    I'm asking for help calculating the actual difference (loss, if any) of locating the Acc/S SSD pair on the x4 slots, hoping to understand how much two mirrored Acc/S SSDs might be better than one (WRITE speeds - same, but READ speeds go to x2).

    the adapter -
    https://eshop.macsales.com/item/Other World Computing/SSDACL6G.S/

    the SSD -
    https://www.amazon.com/Samsung-2-5-Inch-Internal-MZ-75E500B-AM/dp/B00OBRE5UE

    Thanks.
     
  2. h9826790 macrumors G5

    h9826790

    Joined:
    Apr 3, 2014
    Location:
    Hong Kong
    #2
    No performance difference. This OWC card is just a PCIe 2.0 x2 card.

    Even you put two card's in the slot 3 and 4 (which share use PCIe 2.0 x4 lane), there still no performance penalty.

    Anyway, there is some simpler option. Single card for 2 SSDs, which can save you one PCIe slot.

    https://forums.macrumors.com/threads/dual-boot-confirmed-for-new-apricorn-velocity-duo-x2.1721573/

    Also, unless your 280X is wider than dual slot. It should not infringe the other card to go into slot 2.

    Finally, I don't think the Apple software RAID does implant load balancing / optimisation. AFAIK, there is zero read speed improvement in Apple software RAID 1 (but I am not 100% sure on this matter). RAID 1 just "can" provide 2x read speed, but not "will" provide 2x read speed. It depends on the driver / controller.
     
  3. gr8putt thread starter macrumors newbie

    gr8putt

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    #3
    Thanks for your reply.

    I found the Apricorn card on eBay asking $199 + shipping (everybody else is B/O), compared with 2x OWC Acc/S cards shipped for $149. Apricorn shows the card is discontinued, no more support.

    As for RAID.1 READ, I found this on Tom's Hardware site -
    ___
    sub mesa Jun 19, 2009, 2:38 PM
    RAID1 can be just as fast as RAID0 as for reading, because it could read in the very same way as RAID0's do. Better yet, since all disks contain all data, there is no requirement anymore to read from a specific disk; as both disks contain the same data striping can be done more efficiently.

    So, RAID1 should be faster than RAID0 for random read, and at least the same as for sequential read. Unfortunately, only UNIX RAID drivers like geom_mirror implement things like load balancing and round robin algoritms on the RAID1 layer.
    ___

    So there's no info on what MacOSX is doing for load balancing optimization? Couldn't find anything.

    My goal is a mirrored redundancy and some improved READ speed.

    OWC Confirmed using Terminal I can get a RAID.1 using 2 matching PCIe slots on the MacPro5,1 (either the x16 or x4). But if there's no real 2x READ in RAID.1, I could, for less cash, go with a single SSD at twice the size (for longevity) and CCC Backup to an external something.

    As for room above the Radeon, it will be tight putting anything into the upper x16 slot (see pic).
     

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  4. h9826790 macrumors G5

    h9826790

    Joined:
    Apr 3, 2014
    Location:
    Hong Kong
    #4
    I leave the RAID 1 users to answer your question. Or if you have some spare USB drives around, you can setup 2 USB drives in RAID 1 and check if the read speed is improved.

    It’s hard to judge by that photo, but it looks like a dual slot card. Of course, can install a card in slot 2 doesn’t mean it’s a good idea, especially the new card may block the 280X’s fan.
     
  5. gr8putt thread starter macrumors newbie

    gr8putt

    Joined:
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    #5
    As for RAID-ing 2x SDDs on the PCIe buss, it turns out the 2x READ "capacity" is a "sometimes optimal" and can be throttled back by the G3 bus, so no big gain for the $$$.

    The OWC Accelsior S PCIe card arrived and fits in the 16x slot with a good 1/4 inch gap above the Radeon's down-pulling fans - everything is cool to the touch while ccc was cloning from MacHD in bay 1. And there's no issues with 10.13's APFS, as the PCIe SSD appears as an external SATA, so booting next to 4 bays in RAID.10 should be fun.
     

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4 February 19, 2018