On Tue, Jan 29, 2008 at 07:46:58PM +0300, Michael Tokarev wrote: > Keld Jørn Simonsen wrote: > > On Tue, Jan 29, 2008 at 06:13:41PM +0300, Michael Tokarev wrote: > >> Linux raid10 MODULE (which implements that standard raid10 > >> LEVEL in full) adds some quite.. unusual extensions to that > >> standard raid10 LEVEL. The resulting layout is also called > >> raid10 in linux (ie, not giving new names), but it's not that > >> raid10 (which is again the same as raid1+0) as commonly known > >> in various literature and on the internet. Yet raid10 module > >> fully implements STANDARD raid10 LEVEL. > > > > My understanding is that you can have a linux raid10 of only 2 > > drives, while the standard RAID 1+0 requires 4 drives, so this is a huge > > difference. > > Ugh. 2-drive raid10 is effectively just a raid1. I.e, mirroring > without any striping. (Or, backwards, striping without mirroring). OK. uhm, well, I did not understand: "(Or, backwards, striping without mirroring)." I don't think a 2 drive vanilla raid10 will do striping. Please explain. > Pretty much like with raid5 of 2 disks - it's the same as raid1. I think in raid5 of 2 disks, half of the chunks are parity chynks which are evenly distributed over the two disks, and the parity chunk is the XOR of the data chunk. But maybe I am wrong. Also the behaviour of suce a raid5 is different from a raid1 as the parity chunk is not used as data. > > > I am not sure what vanilla linux raid10 (near=2, far=1) > > has of properties. I think it can run with only 1 disk, but I think it > > number of copies should be <= number of disks, so no. I have a clear understanding that in a vanilla linux raid10 (near=2, far=1) you can run with one failing disk, that is with only one working disk. Am I wrong? > > does not have striping capabilities. It would be nice to have more > > info on this, eg in the man page. > > It's all in there really. See md(4). Maybe it's not that > verbose, but it's not a user's guide (as in: a large book), > after all. Some man pages have examples. Or info could be written in the faq or in wikipedia. Best regards keld - 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
