> On Tuesday March 17, goswin-v-b@xxxxxx wrote: > > Hi, > > > > I'm wondering why the kernel requires a raid6 to have at least 4 > > disks (of which at most 2 can be missing). Why not 3 disks? I should think that this is the 'defination' of a raid6. If you build a raid6 resource it should be raid6 and as such be able to tolerate the loss of two disks and all the other raid6 properties. If you build a raidN with three disks that can tolerate the loss of one disk it is not raid6 but raid5 and should be called by the correct descriptive name. The importance of this strictness surfaces in documentation. Both to the system admin working on the system and also documentation from the system admin to his management that is comparing prices and matching features. i.e. "Bob's raid6 is 25% less costly than Fred's". Truth in advertising comes to play. Hidden in this thread is an interesting notion of migration from a "lesser" raid to a more durable raid over time. It might make sense to facilitate limited tools to this end. Even for those sites that wish to stage the construction of a large raid install or to stagger the poweron hours and date codes of drives on the common notion that batches of drives fail together. Or perhaps a "raid6 ready" raid5 that gets populated with the absent drive on the first statistical sniff of an error outside of the norm. Or the arrival of warrenty expiration.... Such a "raidN ready" setup does confuse the notion of operational health for any monitoring tool and is likely a very bad idea for that reason alone. This 2001 URL is interesting in the comments about how unfortunate the choice of the world "level" was. http://www.pcguide.com/ref/hdd/perf/raid/levels/index.htm also interesting is the coment about a vendor being sloppy with the technical language. -- T o m M i t c h e l l Found me a new hat, now what? -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
