Dual-port SAS HDD ?

Ben RUBSON ben.rubson at gmx.com
Thu May 6 15:14:53 UTC 2021

> On 6 May 2021, at 15:51, Alan Somers <asomers at freebsd.org> wrote:
> On Thu, May 6, 2021 at 7:37 AM Ben RUBSON <ben.rubson at gmx.com <mailto:ben.rubson at gmx.com>> wrote:
> > On 6 May 2021, at 15:24, Alan Somers <asomers at freebsd.org <mailto:asomers at freebsd.org>> wrote:
> > 
> > On Thu, May 6, 2021 at 4:52 AM Ben RUBSON <ben.rubson at gmx.com <mailto:ben.rubson at gmx.com> <mailto:ben.rubson at gmx.com <mailto:ben.rubson at gmx.com>>> wrote:
> > Hi,
> > 
> > I'm building a new ZFS pool from scratch, choosing my own hardware etc...
> > For sure I'll go for the standard SAS2008 / SAS3008 controller.
> > 
> > However, I'm wondering whether or not I should absolutely go for dual-port SAS HDD (with dual backplane, controller...).
> > I have some difficulties to find enterprise grade dual port SAS HDD.
> > HGST used to provide Ultrastar SAS HDD which were dual-port.
> > However, strangely, Western Digital does not advertise their Ultrastar DC SAS HDD as bringing dual-port, so I guess they're not.
> > 
> > Any thoughts / advices regarding this topic ?
> > 
> > Many thanks for your help,
> > 
> > Kind regards,
> > 
> > Ben
> > 
> > It's just a matter of high availability.  Can you tolerate an outage if a JBOD I/O controller fails?  If so, then you don't need dual-port.  But server crashes are more common than JBOD I/O controller failures.  So you should worry more about that.
> Thank you Alan.
> Of course you're right, JBOD IO controller is not the first outage cause, and disks themselves are more prone to fail...
> I even wonder whether or not dual path is actively used for HDDs, as dual-port ones are rather hard to find...
> Not sure then it's really worth it...
> Of course feel free if I'm wrong / I missed something / one actively uses it and has some experience / references to share !
> Thank you again,
> Ben
> Sure, dual paths are actively used.  They work well with gmultipath, which is how I use them.  And AFAIK all SAS drives are dual-ported.  Western Digital describes their drives as "dual port" on this site:
> https://www.westerndigital.com/products/data-center-platforms/ultrastar-sas-series-ssd <https://www.westerndigital.com/products/data-center-platforms/ultrastar-sas-series-ssd>
You're right, SAS SSDs are dual-port.
However, their SAS HDDs are not advertised as such :
So I wonder.


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