Date: Thu, 6 May 2021 07:51:49 -0600 From: Alan Somers <asomers@freebsd.org> To: Ben RUBSON <ben.rubson@gmx.com> Cc: "fs@freebsd.org" <fs@freebsd.org> Subject: Re: Dual-port SAS HDD ? Message-ID: <CAOtMX2h%2BDjXYkDGHQFuw_adabiGiaU9XN2FPXheutMWL=UPN1w@mail.gmail.com> In-Reply-To: <62B46E11-A40C-4119-8525-20E3F3539D61@gmx.com> References: <578487FF-1D89-4A9E-AD97-6B5DCD9F785A@gmx.com> <CAOtMX2jgrmbEefg2pJ55Bp1bJDzC3tgyjUK5%2BopvCt75T3_NDw@mail.gmail.com> <62B46E11-A40C-4119-8525-20E3F3539D61@gmx.com>
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On Thu, May 6, 2021 at 7:37 AM Ben RUBSON <ben.rubson@gmx.com> wrote: > > On 6 May 2021, at 15:24, Alan Somers <asomers@freebsd.org> wrote: > > > > On Thu, May 6, 2021 at 4:52 AM Ben RUBSON <ben.rubson@gmx.com <mailto: > ben.rubson@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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