On Tuesday November 18, jim@jimtreats.com wrote: > Hi folks.. > > hopefully everything will be working soon and i can get on with trying to > get some backup scripts working :) > > I am going to stick with this software RAID for the near future if it > carries on working correctly.. I was just wondering what peoples views were > of software vs hardware raid... anything and everything really.. I'm not > that up on all the technology... I know that 3ware have a good rep in > hardware... I also imagine that for more exotic RAID configurations its > obviously a help to not stress the CPU with the RAID tasks.. for me tho with > simple mirroring the CPU costs are minimal.. the linux core is a sturdy base > to build upon so is software raid in this way a perfectly acceptible > reliable RAID solution.. > > Just curious.. Not an easy question to answer. RAID is all about surviving failures, and there are alots of possible failure modes, some more predictable than others. The obvious failure modes are handled perfectly well by all solutions. The less obvious failure modes are probably handled as best as possible by all solutions, but with these, the question is usually "how can I recover", and the answer there depends on how much support you can get, and how much you can work out yourself. For support: linux-raid is an adequate support community, but there is no guarantee of instant support. I don't know what support there might be around various hardware raid solution. Again, someone on linux-raid might be able to help, or they might not. For "how much you can work out yourself", that depends partly on you. Your hardware raid might come with good doco, or it might not. Software RAID somes with assorted bits of doco, and complete source. You are part of your system, and system reliability depends in-part of how much you know. With software raid you can learn as much as you want to, but it might require more work that you care to put it. Software raid can be affected by lots of parts of the system. Reliability of hardware raid is more tightly connected to the controller and drives. As examples of "less obvious failure modes": I had a mirrored pair that kept getting data corruption. It turned out that one of the drives had a bad bit in an internal buffer, and would occasionally return 1 for the 12th bit (or similar) of each sector even when it should be zero. Neither software raid or hardware raid would cope with that. Some people find that their IDE controller works fine until they try to use RAID1. RAID1 hits multiple discs concurrently a lot, and some (few, specific) ide controllers don't appear to cope. You probably would not get that with hardware raid. You can with software raid because it is a "whole-system" thing. I prefer software raid because I like the fact that I can see inside and understand it completely. Some people like hardware raid because "it just works". Both are valid perspectives and as you, the sys-admin, are part of the system, your prespective and opinion is a significant part of what makes the system "reliable". NeilBrown - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
