Multiplying SAS ports without backplane?

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rumpelstilz

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May 27, 2022
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I would like to connect 16 drives to an onboard LSI SAS2308 6Gbps HBA. The HBA is present on my X9SRH board in form of blue SATA-style connectors, eight of them.

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Would it be possible to "multiply" these 8 ports, so I can connect more than 8 drives, without having to use a backplane?
It's my first time working with SAS, so I'm not entirely sure if what I want is even possible. I was hoping I could use an adapter like this for the job:

1694196111248.png

(i.e. attach this board to a SAS HDD, connect my onboard ports to "primary", and connect an additional drive via "secondary")

Assuming this would work, do I need any special data cables with my onboard SAS connectors, or are these compatible with SATA data cables?
And would the 2nd drive also need to be a SAS drive, or could I connect a SATA drive to the "secondary" port?
Thanks for the help!
 

BlueFox

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Oct 26, 2015
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The adapter you linked is not for daisy-chaining drives (which is not a thing with any type of disk). SAS disks have 2 ports and that exposes both to be uses with breakout cables.

You need a SAS expander if you want to attach more drives. An example would be an Intel RES2SV240.

You'll find that unless you are using the integrated RAID functionality, it's cheaper to just get another SAS or SATA HBA than an expander. You already have 14 ports on the motherboard, assuming you are using SATA drives.
 

rumpelstilz

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May 27, 2022
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Unfortunately I don't have any i/o left, and I need those SATA ports elsewhere, so I'll have to use an expander.

Can I attach my SATA-style SAS connectors to the Intel Expander with a typical "SFF-8087 to 4x Latching SATA" breakout cable? Do they work in both directions? Is there a particular brand of cable I would have to use (LSI/Broadcom)?

And if I understand this correctly, the PCIe connection on that Intel Expander is completely optional, it only needs power, either from 4-pin or PCIe?
 

mrpasc

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Jan 8, 2022
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You need a „reverse breakout“ cable, some better vendors / shops mark them as 4x Sata (Host) to SFF-8087 (Target). Those cables do not work in both directions, so double check before buy.
And yes, the PCIE connection is just for power, if you power via 4-Pin you can lay the card wherever is suits in your case.
 

Sean Ho

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What case are you using? Do you have an expander backplane?

If you're directly connecting to drives without a backplane (e.g., in a consumer tower case), you'll need two reverse breakout cables (4xSATA to 8087), then a SAS expander (such as the Intel one, the venerable HP 487738-001, or SAS3 AEC-82885), then as many forward breakout cables as you need (8087 to 4x 8482). You'll also need SATA power to the drives, with 3.3v line removed to avoid SATA PWDIS.
 

rumpelstilz

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May 27, 2022
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Thank you all for the advice!

I don't have a backplane and would like to use a Fractal Define tower case. If I'm using an expander card, I will probably stick to SATA HDDs.
With a reasonably modern PSU and SATA drives (all 2020+), does your advice still apply? Would I loose any relevant drive-related functionality without PWDIS?
I was going to passthrough the SAS controller to a TrueNAS VM.
 
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nexox

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May 3, 2023
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SATA drives don't support the SAS error reporting protocol, so when they're behind an expander you may get an error up to the OS level and have no idea what drive it came from.
 

Sean Ho

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But SATA drives will report SATA errors just fine via STP across the SAS HBA. With this little density, OP can mix and match SATA and SAS drives freely without much performance impact.

If 3.3v is not removed, the risk is that the drives will simply not initialize.
 

nexox

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May 3, 2023
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But SATA drives will report SATA errors just fine via STP across the SAS HBA.
My experience, and that of others however long ago I checked (the SATA spec hasn't changed since,) is that this doesn't work once you have a SAS expander in between the drives and HBA.
 

mattventura

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Nov 9, 2022
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As said, you'd need a "reverse breakout" to connect the individual SAS ports on the motherboard to a 4-lane connector on an expander. Good expanders are very cheap nowadays (<$25 for an 82885T). Also claims to support STP according to the manual, though I only run SAS drives on mine.
 

Sean Ho

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My experience, and that of others however long ago I checked (the SATA spec hasn't changed since,) is that this doesn't work once you have a SAS expander in between the drives and HBA.
Are there particular SATA errors you're thinking of? I have an ancient HUA723020 (SATA 2TB) on SAS2-EL2 to 9211, and I can see SMART attributes like 198 (offline uncorrectable) and an ATA error log including a series of CRC errors from back when I had a faulty cable. If you have a specific command you'd like me to run against my drive, I'd be happy to. Not trying to change your mind, just offering information.
 

nexox

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SMART is fine, it's things like read and write errors as they happen, the kind of messages that indicate to RAID controllers that they should kick out a disk. I was lucky and managed to stop my array then check SMART to find the bad drive, others I know had the controller shoot the wrong drive(s), then the failing drive fully died and they were left with inconsistent devices to recover as much as they could.

I have seen some references that some SAS3 expanders might handle this better than the SAS1 and 2 expanders involved in the issues I know about, but since manufacturers don't really talk about it to begin with it's hard to find anything specific.
 

nexox

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I was using md software RAID, probably why it didn't end in total corruption, hardware RAID seemed to make worse choices, but it's still the same issue and manifested the same with md, errors that weren't associated with any particular disk, I think the kernel printed the HBA port, which would have been fine when directly connected, but was pretty useless with an expander.