Date: Mon, 06 Nov 2017 04:09:28 -0600 From: "Zane C. B-H." <vvelox@vvelox.net> To: Alan Somers <asomers@freebsd.org> Cc: "Mikhail T." <mi+m@aldan.algebra.com>, FreeBSD-scsi <freebsd-scsi@freebsd.org>, freebsd-hardware@freebsd.org, owner-freebsd-hardware@freebsd.org Subject: Re: Do I need SAS drives?.. Message-ID: <cd7ab44859b519b9f78fa84cb43ef4ff@vvelox.net> In-Reply-To: <CAOtMX2jeUbSm535Zvd_7aHfQao-dMs5zbU0o3GRWk%2BcmW1Nq=g@mail.gmail.com> References: <4DFBCE11-913A-4FC9-937D-463B4D49816C@aldan.algebra.com> <CAOtMX2jeUbSm535Zvd_7aHfQao-dMs5zbU0o3GRWk%2BcmW1Nq=g@mail.gmail.com>
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On 2017-08-09 10:59, Alan Somers wrote: > On Wed, Aug 9, 2017 at 8:27 AM, Mikhail T. <mi+m@aldan.algebra.com> > wrote: > 1) When a SATA drive goes into error recovery, it can lock up the bus > indefinitely. This won't matter if your drives are directly connected > to a SAS HBA. But if you have an expander with say, 4 SAS lanes going > to the HBA, then a flaky SATA drive can reduce the bandwidth available > to the good drives. In my years of doing decade plus of DC work, I've seen both SAS and SATA drives flake and render systems in operable till the offending drive is removed. > 4) The SAS activity LED is the opposite of SATA's. With SATA, the LED > is off for an idle drive or blinking for a busy drive. With SAS, it's > on for an idle drive or blinking for a busy drive. This makes it > easier to see at a glance how many SAS drives you have installed. I > think some SATA drives have a way to change the LEDs behavior, though. HPs and Dells will show on by default, regardless of if it is SATA or SAS. For Supermicro it will vary between backplanes. > I'm guessing that you don't have an expander (since you only have 8 > slots), so item 1 doesn't matter to you. I'll guess that item 3 > doesn't matter either, or you wouldn't have asked this question. Item > 5 can be dealt with simply by buying the higher end SATA drives. So > item 6 is really the most important. If this system needs to have > very high uptime and consistent bandwidth, or if it will be difficult > to access for maintenance, then you probably want to use SAS drives. > If not, then you can save some money by using SATA. Hope that helps. Actually most boxes with more than 4 slots tend to be use multipliers. As to uptime, that is trivial to achieve with both. With both it is of importance of drive monitoring and regular self tests.
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