Date: Sat, 27 Jun 1998 19:31:09 -1000 From: richard@pegasus.com (Richard Foulk) To: freebsd-hardware@FreeBSD.ORG Subject: Re: RAID and FreeBSD Message-ID: <199806280531.TAA26134@pegasus.com> In-Reply-To: Greg Lehey <grog@lemis.com> "Re: RAID and FreeBSD" (Jun 28, 1:23pm)
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} > Even if you upgrade your RAID box (which happens much less often than } > OS upgrades in my experience), the system is simpler } } That's a valid point. } } > and the RAID is much more likely to be just like the vendors units. } } I don't understand that. What are you saying? Software RAID, implemented as a device driver, is an integral part of the OS kernel. The kernel is a large collection of device drivers and tools for accessing hardware. With Unix that collection is different on just about every host that runs it -- due to so many different hardware configurations. } } > With OS-based software RAID you'll almost never have a configuration } > just like the vendor's. } } I still don't understand. Are you saying that configurability is a } disadvantage? } No. Complexity is a disadvantage. I look at RAID as a large repository for treasures that are collected over time. The host system is the toolset used to mine those treasures. The toolset is constantly being revised and updated as we devise better ways to manipulate the data. Though the data on the RAID is probably being revised and updated too, the means of storing it probably isn't. RAID is a powerful way of scattering large amounts of bits among a collection of disks. It raises my comfort level to be able to say that that complex system has been working reliably (unchanged) for so many months and I have reason to expect that it will continue doing so. Unix is a fabulous operating system that does many things quite well. One of it's shortcomings is that the kernel is usually one large monolithic program which combines all of it's device drivers together in the same address space. Any driver is free to scribble in the code or data of any other. So unlike a hardware RAID which is relatively simple and well-tested in comparison. The various Unix device drivers that one implementation brings into play may not even have been used together before. Being of widely varying pedigree, maturity and level of testing, any one of these drivers is free to modify the guts of the software RAID engine directly. Free to change the way the mass data spew amplifier (RAID) throws it's data around. When it's working correctly the RAID spreads data among it's drives pretty wildly. Change a bit or two in one of it's algorithms and look out! If the driver or associated hardware for your video, keyboard, mouse, cd-rom, sound-card or printer malfunctions you fix it and go back to work. If your RAID fails, some of your hard-won treasure may be lost forever. Richard To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hardware" in the body of the message
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