Date: Sat, 29 Apr 2000 13:13:37 -0700 From: Mike Smith <msmith@freebsd.org> To: "Brandon D. Valentine" <bandix@looksharp.net> Cc: Mark Powell <M.S.Powell@salford.ac.uk>, Joe Karthauser <joe@pavilion.net>, freebsd-stable@FreeBSD.ORG Subject: Re: How good is AMI MegaRAID support? Message-ID: <200004292013.NAA01003@mass.cdrom.com> In-Reply-To: Your message of "Sat, 29 Apr 2000 12:31:51 EDT." <Pine.BSF.4.21.0004291208080.20399-100000@turtle.looksharp.net>
next in thread | previous in thread | raw e-mail | index | archive | help
> On Fri, 28 Apr 2000, Mark Powell wrote: > > >I appreciate the good work Simon and Mike are doing in this area. However, > >I wanted to know what is the current RAID solution of choice for FreeBSD. > >As I'm sure you understand I need a proven solution. > > I can definitely appreciate that. The RAID solution of choice for > FreeBSD appears to be SCSI-SCSI RAID adapters as utilized on > wcarchive.cdrom.com and ftp.freesoftware.org -- the two busiest ftp > archives around and consequently the two busiest disk subsystems around. That's both debatable and highly hyperbolic. It also entirely denies the reality that no one solution is appropriate for an entire class of problems. In many situations, the lower cost and higher performance of an 'embedded' RAID controller make it a much better solution. > Both of these configations utilize the latest Adaptec 78xx based PCI > SCSI controller attached to a SCSI-SCSI RAID adapter. Unless I'm mistaken, neither of them are using U160 controllers. > In the case of > wcarchive it is a Mylex DAC960SXI SCSI-SCSI 6 channel RAID controller, > w/256MB cache. ftp.freesoftware.org doesn't reveal to us what sort of > SCSI-SCSI RAID controller is in use but I would assume it's the same or > similiar to wcarchive since TeraSolutins, Inc. had a hand in both > systems. JFYI, Tera are no longer recommending or using the Mylex SCSI:SCSI controllers. > This approach does offer a layer of protection from scsi > controller obsolesences or driver bitrot. You put a relatively cheap > well supported SCSI controller in your machine and interface it to your > external RAID canister. That controller can be replaced and upgraded as > necessary while still keeping the same disk subsystem behind it. It > also allows you to forget about bugs in the raid code or availability of > something like mlxcontrol since it's all handled in hardware. This isn't the whole picture, unfortunately. - You lose bandwidth and throughput by using a SCSI interface. (You can recover some of this using multiple SCSI busses, but do the math; how many LVD SCSI channels do you need to match a 64-bit 66MHz PCI slot?) - You are still at the mercy of the firmware in the RAID adapter, whether it be internal or external (see above inre: Tera not liking Mylex anymore). - You still need an array management tool. > You can > also attach multiple hosts to the RAID canister, allowing more than one > system to use the same disks. That can also come in handy if you need > redundant servers but don't want to mirror all of your content. This is largely irrelevant, since it's possible to do the same thing with a PCI:SCSI RAID controller, but we lack the filesystem technology to do anything useful about it. > The decision all comes down to just how future proof you need to be and > how much money you have to sink into your project. You leave out "how well you want it to perform" as well. All other things being equal, the PCI:SCSI adapters will give you better bang for your buck. -- \\ Give a man a fish, and you feed him for a day. \\ Mike Smith \\ Tell him he should learn how to fish himself, \\ msmith@freebsd.org \\ and he'll hate you for a lifetime. \\ msmith@cdrom.com To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-stable" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?200004292013.NAA01003>