Dual-port SAS HDD ?

Alan Somers asomers at freebsd.org
Thu May 6 13:52:02 UTC 2021


On Thu, May 6, 2021 at 7:37 AM Ben RUBSON <ben.rubson at gmx.com> wrote:

> > On 6 May 2021, at 15:24, Alan Somers <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>> 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


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