Date: Tue, 26 Aug 1997 23:03:15 -0700 (PDT) From: Tom <tom@uniserve.com> To: "Michael L. VanLoon -- HeadCandy.com" <michaelv@MindBender.serv.net> Cc: FreeBSD <freebsd@synertec.ene.unb.br>, stable@freebsd.org Subject: Re: DPT scsi card Message-ID: <Pine.BSF.3.96.970826225741.12208E-100000@shell.uniserve.com> In-Reply-To: <199708270529.WAA25841@MindBender.serv.net>
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On Tue, 26 Aug 1997, Michael L. VanLoon -- HeadCandy.com wrote: > >On Tue, 26 Aug 1997, Michael L. VanLoon -- HeadCandy.com wrote: > >> You can do RAID in software with the ccd (concatenated disk) driver. > >> There are FreeBSD and NetBSD servers running this all over the place. > >> It's rock solid extremely fast. > > > I wouldn't call ccd a RAID solution. The "R" in RAID stands for > >redundant, and ccd has poor support for that. > > While that was the original "definition", RAID had become to be known > for more than simple redudancy in common usage. Striping without > fault tolerance is a very common usage, which generally falls under > the term "RAID-5", if I'm not mistaken. Err.. no. Striping without reduncancy has become known as RAID-0. > From what I understand, ccd can be used for mirroring. However, > recovery in case of failure is not automatic, and you can't mix > mirroring with striping. > > So, yes, if you're using ccd to stripe for performance, you don't get > any redundancy features with ccd. If you use it for mirroring, it's > likely that you won't get any performance benefits. ccd should be able to improve read performance while reading, but I don't know if it does. > DPT controllers are reported to do all that stuff transparently in > hardware. And, the FreeBSD driver supports basic functionality on DPT > cards. However, it isn't clear how much advanced functionality the > FreeBSD DPT driver supports. > > ----------------------------------------------------------------------------- > Michael L. VanLoon michaelv@MindBender.serv.net > Contract software development for Windows NT, Windows 95 and Unix. > Windows NT and Unix server development in C++ and C. > > --< Free your mind and your machine -- NetBSD free un*x >-- > NetBSD working ports: 386+PC, Mac 68k, Amiga, Atari 68k, HP300, Sun3, > Sun4/4c/4m, DEC MIPS, DEC Alpha, PC532, VAX, MVME68k, arm32... > NetBSD ports in progress: PICA, others... > ----------------------------------------------------------------------------- > Tom
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