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How to connect eg 16 drives to LSI MegaRaid?

Discussion in 'Storage' started by Zapador, Jul 22, 2012.

  1. Zapador New Member

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    Hi.

    According to LSIs website - http://www.lsi.com/products/storagecomponents/Pages/MegaRAIDSAS9265-8i.aspx - this RAID controller supports up to 128 drives.

    But I can't figure out how to connect more than 8.
    It has 2x SFF-8087 connectors which each supports 4 drives - so 8 in total.

    I have been unable to find cables that support more than 4 devices each. Also I cannot find any expanders or similiar.

    What to do?

    Thank you.
  2. Kreij

    Kreij Senior Monkey Moderator Staff Member

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    I would assume you would need something like this.
    Zapador says thanks.
  3. Zapador New Member

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    I guess you're right about that.
    But since its a PCIe card that would make me unable to use more than 8 drives, as I don't have any free PCIe slots.

    Any chance for another solution - anyone? :rolleyes:
  4. newtekie1

    newtekie1 Semi-Retired Folder

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    The PCIe part of the card is just a dummy to help secure the card in the computer, you can really mount it anywhere you want without needing a PCIe slot.

    But I believe you can use any SAS port multiplier.
    Crunching for Team TPU 50 Million points folded for TPU
  5. Jizzler

    Jizzler

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    Can chain several of these 8 x 2.5" units: http://www.supermicro.com/products/accessories/mobilerack/CSE-M28E2.cfm

    You can buy cases which have upwards of 36 (3.5") or 72 (2.5") drive bays connected to a SAS backplane. The controller would connect via those two cables to the backplane.

    Now if you get the external version of that LSI controller, Norco makes a very cheap 24-bay case with single SFF-8088 in:
    http://www.norcotek.com/item_detail.php?categoryid=8&modelno=ds-24er


    Some options are better than others, depending on if you already have the card or not, and your storage goal/purpose.
  6. Zapador New Member

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    Thanks for all your good advice.

    What I want to do is have a total of 12 drives in my workstation, 8 SSDs in a RAID5 for sys/swap and another 4 HDDs in RAID5 for the storage.
    So I would like it all to be internal, but it seems I'll have to investigate a bit further.
  7. The Von Matrices

    The Von Matrices

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    Buy an Intel RS2SV240, like I did for my server. Its the cheapest I could find on the market and works great in my server.
    Zapador says thanks.
  8. Zapador New Member

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    Oh, that seems like a good solution.

    Do you know if such a card is likely to impact speed or not?
    I would be quite saddened by suddenly ending up in the sub-2GB/s spectrum of speed ;)
  9. The Von Matrices

    The Von Matrices

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    I am using 3TB mechanical drives in RAID 6, so I can't tell you from experience if there are any slowdowns since the drives are slower than the interface anyway.

    The only bottleneck would be the SAS uplink from the expander to the RAID card. It's 4 x 6Gb/s links, so 24Gb/s (3 GB/s) maximum theoretical bandwidth from everything attached to the expander combined. If you're using 8 SSDs, I would connect 4 of the SSDs to the open port on the RAID card and the other 4 SSDs to the expander in order to have the least chance of experiencing a bottleneck. Connect the 4 HDDs to the expander since they don't have a huge bandwidth requirement anyway.

    Also, if you're using anything other than RAID 0, I wouldn't expect multiple GB/s transfer rates that you are talking about since the computational power of the controller will be limiting factor.

    Here are pictures of my server, in case you are wondering about configuration. The 8 mechanical drives (in RAID 6) are attached to the Intel RES2SV240 expander, which is attached to the Intel RT3WB080 SATA controller. I also have 2 SSDs in RAID 1 attached to the controller serving as a SSD CacheCade. Note that I don't actually have the expander card in a PCIe slot; it mounted to the bottom of the case and is powered by a molex connector.

    [​IMG]
    [​IMG]
    [​IMG]
    theeldest says thanks.
  10. Zapador New Member

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    Thx a bunch Matrices for clarifying the stuff this well! :toast:

    Concerning the 2+ GB/s, I forgot to add that its read speed and definitely not write.
    Having looked at benchmarks with this specific RAID controller (LSI 9265) and 8x SSDs attached it seems very possible (or is possible) to get a read speed of over 2 GB/s.

    I wasn't sure how to calculate the maximum bandwidth for a SAS expander, but its pretty straight forward I see. Since the drive has a theoretical max read of 550 MB/s ~ 4400 Mb/s it seems unlikely that it should bottleneck.

    Once again, thanks to everyone.

    I've come to the conclusion that I will initially build my workstation with 5 SSDs and 3 HDDs to save on initial cost and then expand it when needed. The 5 SSDs running in RAID5 for increased read performance and data security, and the 3 HDDs also in RAID5 with the bearable 1/3 cut in capacity. This gives me storage and speed right now at a manageable price.

    :)

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