On Wed, Feb 08, 2012 at 06:56:03PM -0800, Qrux wrote: > > On Feb 8, 2012, at 6:00 PM, Ken Moffat wrote: > > > I've used SW RAID-1 for several years : my impression is that the > > change happens in mdadm, rather than the kernel, and that (so far) > > backwards-compatability has been a major consideration. > > I think there's some level of kernel support: > > xlapp-linux-3.1-kernel.config:CONFIG_MD_AUTODETECT=y > xlapp-linux-3.1-kernel.config:# CONFIG_MD_LINEAR is not set
Yes, there is certainly kernel support. The point I was trying to make is that user-visible change happens in the userspace part (mdadm). > But, even if the disk format is only controlled by mdadm, you still count on > people doing "TheRightThing(TM)" and making sure backwards compatibility is > there. That's the same as with hardware vendors. They have investments, > too, and some companies are quite friendly to the Linux community (e.g., > 3ware, at least before the AMCC/LSI acquisition). I'm just saying that's a > very similar argument for both HW and SW, and doesn't necessarily favor one > over the other. > Agree. > > A recovery HOWTO might be useful (for RAID-1, the hardest part is > > actually making sure you have identified the bad drive - using > > different brands of drive [ if there is a choice ] can help!). For > > Different drives for RAID-1? I'm not sure that should go into the book. > It's probably enough to say: "Make sure you have the right drive in a > recovery scenario." > > I'm of the school that the drives should be as similar as possible. > [ snipped the interesting explanation ] We have different use cases - I'm an individual buying consumer hardware from the local supplier(s). For a long while, consumer-grade drives went through a good patch (after the 'deathstar' period), but in the last year I've had two different drives fail on the (new) machine I use as my server. One was the unmirrored root disk, the other was in the RAID. And different brands. In those circumstances, for a RAID array there is (in my opinion) an argument for using drives from different batches. In the consumer market, drives seem to change rapidly - if you buy two this week, they will be the current version, in a month's time - if something *nominally* the same is even available - it may be completely different. So, in practice I'm happy to mix manufacturers in the hope that I'll have been able to replace the next drive that fails before the next-but-one fails. ĸen -- das eine Mal als Tragödie, das andere Mal als Farce -- http://linuxfromscratch.org/mailman/listinfo/blfs-dev FAQ: http://www.linuxfromscratch.org/blfs/faq.html Unsubscribe: See the above information page
