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TL;DR Server's original SAS HBA (PCIe card) does not support transparent passthrough, which is desired, as I want the OS to manage the disks (ZFS).

At my company, we have an Intel SSR212MC2 server (spec sheet) with SRCSAS144E RAID controller. The machine is lying around unused, and I was planning to do some experimentation on it before possibly deploying it.

Apparently the SRCSAS144E controller only supports presenting RAID volumes to the OS. Creating twelve single-volume RAID0 groups seemed very inelegant to me, a suspicion confirmed when I realized that the disks wouldn't be able to be moved to another server (see accepted answer of hba for software raid).

So, if my limited understanding of SAS is correct, I could buy another card (such as this), put it in place of the existing one, and plug the cable coming from the SAS expander into it. At the end of the day, the operating system should then see each individual device, right?

The Linux kernel will need drivers to talk to the card, but I assume there is mainstream support for such a commonplace device. Is there anything else I should watch out for?

Nubarke
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  • if it only supports presenting RAID volumes, it is not a HBA card per definition. This means your question title is wrong. It is a RAID card - a HBA will ALWAYS pass through at least optionally. – TomTom May 03 '18 at 15:32

2 Answers2

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You can configure a set of single disk RAID0 LUNs. Assuming you'll turn RAID controller cache OFF it should be acceptable equivalent of a pass-thru mode.

BaronSamedi1958
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    May or may not - Adaptec for example writes metadata on the disc, so a Raid 0 LUN is NOT identical to a raw disc. – TomTom May 03 '18 at 15:33
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    There’s no such a requirement as “raw disk” (BTW, it’s DISK and not DISC) or 1:1 mapping or whatever. Bottom line: If you can remove cache from write path to ensure atomic writes - everything will work just fine. – BaronSamedi1958 May 04 '18 at 16:57
  • Read this: https://storage.microsemi.com/en-us/support/infocenter/release-2016-1/topic/maxview_arcconf_readme.xml/topics/topics/raw_device.html – TomTom May 04 '18 at 16:59
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    I can only repeat what I've told already: Regardless of what a) SDS stack vendor, and b) RAID controller vendor, are both telling you... If there's no write-back cache within the write path everything will work flawlessly. – BaronSamedi1958 May 22 '18 at 12:51
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You can just use a standard LSI/Avago SAS HBA for this purpose. That's all that's necessary.

Since this is an old server... 11 years old, you should see a controller that is period-correct. I'd recommend a used LSI 9211-8i.

No drivers are needed; these are standard MPT Fusion kernel modules. You will need to figure out what to do with the operating system, though. I don't recommend ZFS for the OS drives. So you may need software RAID for that.

ewwhite
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  • Thanks for your answer. I am aware that it is unwise to boot from ZFS; the server has internal 2.5-inch drives for the purpose of storing the OS (a very welcome find!). – Nubarke Apr 29 '18 at 21:45