SAS2308 vs 2008 - any big value in upgrading, besides PCIE b/w?

Discussion in 'RAID Controllers and Host Bus Adapters' started by TheBloke, Mar 10, 2017.

  1. TheBloke

    TheBloke Active Member

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    Here's my question in a nutshell: what are the benefits, if any, in upgrading SAS2008 cards to SAS2308 cards, besides offering PCIE 3.0 bandwidth and being capable of handling more devices (1024 vs 512)?

    If you had a server that only supported PCIE 2.0, containing several SAS2008 cards running a ZFS (or other SWRAID) array on 7200RPM HDDs, and saw some cheap used 2308 cards, would you buy the 2308s and sell the 2008s?

    Here's my full situation and background in more detail:

    I'm in the process of upgrading my home file server. Server is a LGA1366 mobo (Tyan S7012) with 2 x X5670 6-core 2.93ghz CPUs and 72GB of 1333mhz RAM. Running Solaris 11.3, but I'm also considering OmniOS.

    I plan to run a 24 x 2TB ZFS pool (not yet decided between 2 x 12-drive RAIDZ2, 3 x 8-drive RAIDZ2 or 4 x 6-drive RAIDZ2), plus boot SSD and a spare or two, from a total of 28 drive bays:
    • 12 internal : Chenbro 2U chassis, 3 x 4-port SAS/SATA backplanes via 3 x SFF8087 ports
    • 16 external: no-name 3U chassis, 4 x 4-port SATA backplanes via 16 x SATA ports, cabled as 4 x 8087-4xSATA cables through 2 x dual 8087-8088 brackets and then 8088 cables to the server.
    I'm accessing these with quite a mix of LSI cards (dependent on what was easiest and cheapest to buy), all installed in PCI-E 2.0 x8 slots. All cards are running the latest v20 IT firmware.
    • 12 x internal ports:
      • 1 x 9211-4i (SAS2004) - 4 ports, 1 x 8087
      • 1 x 9201-8i (SAS2008) - 8 ports, 2 x 8087
    • 16 x external ports:
      • 1 x 9207-8e (SAS2308) - 8 ports, 2 x 8088 out to the 3U chassis
      • 1 x 9201-8i (SAS2008) - 8 ports, 2 x 8087 going to internal 8087-8088 bracket then 2 x 8088 out to the 3U chassis
    I've just seen an eBay listing for several 9205-8e cards (2308 chipset). I am definitely going to buy one, to replace the 9201-8i I have on my external ports (removing the need for the internal 8087-8088 bracket and 2 x internal 8087 cables.)

    But I am wondering if I should in fact buy two, and also replace one of my internal-port cards - which would require re-using that 8087-8088 bracket to convert the 8e card to an 8i, looping 8088 cables back into the Chenbro chassis (a bit messy, but do-able and I have all the necessary components.) Or I may be able to find a used 8i 2308 card if I keep looking a little longer, which would be the ideal config: two internal cards, two external, no messy converters or extra cables.

    So what I'm wondering is whether there is actually any major benefit in upgrading a 2008 to a 2308? Is it worth going to the hassle of buying a new card and selling an old one, when I can't benefit from the main feature of PCI-E 3.0 bandwidth and I won't use anywhere near the 1024 devices the 2308 now supports?

    But maybe there any other benefits? I do know from personal experience that a FW/BIOS install on the 2308 runs in a couple of seconds compared to much longer on the 2008s. So that suggests it's a decent upgrade in processing power? But does that translate into any noticeable benefits in day-to-day use?

    But I'm not using SSDs - only 7200RPM 2TB HDDs (16 x SATA3, 8 x SATA2) - so quite possibly I have no real need to look at faster HBAs?

    Any info and advice would be gratefully received!

    TB
     
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  2. cheezehead

    cheezehead Active Member

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    SSD's are where you'll get bottlenecked by the 2008 controller. You might still with hard drive caches technically, but i doubt it's noticeable. If your going from multiple 4-port cards to a single card, you might see some power savings. Beyond that someone else can chime in, I haven't had much experience with the 2308 personally.
     
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  3. TheBloke

    TheBloke Active Member

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    OK thanks a lot. Yeah I don't think I'll be limited for bandwidth on the 2008s. I will be running at most 8 x 7200RPM SATA3 HDDs from each 2008, and based on the 2008's bandwidth figures (eg 3433MB/s max throughput, from the LSI thread) I won't come close to using even half of that.

    So from a bandwidth perspective I can see there's not much point. I was wondering if there were any other benefits to the faster processing or to the newer chipset. But I don't know what that could be really given I'll be running it in IT mode - using almost none of the card's processing ability - so quite likely there's really no other benefit. Except for saving 20 seconds per FW update! :)

    Thanks again.
     
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  4. cheezehead

    cheezehead Active Member

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    It takes a lot of spinners to botteneck out a 2008 controller. The bigger issue is when you introduce SSDs, it's pretty easy to max out the 290k IOPS on that controller, the 2308 is a bit better but 600k IOPS vs SSDs still doesn't take many. With ZFS and even using SSD's for caching you could always hang them off of a different bus to work-around the limits and keep the spinners behind the 2008 controller as well.
     
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  5. vanfawx

    vanfawx Active Member

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    The biggest different on my end between a 2308 and a 2008 is the 2308 get at least 8 MSI-X interrupts compared to the single MSI-X interrupt the 2008 card gets. This allows it to spread IO across multiple cores. This should help when using SSD's on this card. As well as others have said, the 2308 card is PCIe 3.0 vs PCIe 2.0 for the 2008.
     
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