Dual-port SAS HDD ?

[Alan Somers]

On Thu, May 6, 2021 at 9:14 AM Ben RUBSON <ben.rubson at gmx.com> wrote:

>
>
> > 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 :
>
> https://www.westerndigital.com/products/data-center-platforms/ultrastar-dc-hc600-series-hdd
>
> https://www.westerndigital.com/products/data-center-platforms/ultrastar-dc-hc500-series-hdd
> So I wonder.
>
> Ben
>

Oh, good point.  I don't know.  You could always ask.  I use mostly Seagate
dual-ported HDDs.
-Alan