On Tuesday, April 08, 2014 03:47 AM, Rafał Radecki wrote: > As far as I know raid10 is ~ "a raid0 built on top of two raid1" ( > http://en.wikipedia.org/wiki/Nested_RAID_levels#RAID_1.2B0 - raid10). So I > think that by default in my case: No, Linux md raid10 is NOT a nested raid setup where you build a raid0 on top of two raid1 arrays. > > /dev/sda6 and /dev/sdb6 form the first "raid1" > /dev/sdd6 and /dev/sdc6 form the second "raid1" > > So is it so that if I fail/remove for example: > - /dev/sdb6 and /dev/sdc6 (different "raid1's") - the raid10 will be > usable/data will be ok? > - /dev/sda6 and /dev/sdb6 (the same "raid1") - the raid10 will be not > usable/data will be lost? The man page for md which has a section on "RAID10" describes the possibility of something is absolutely impossibe with a nested raid1+0 setup. Excerpt: If, for example, an array is created with 5 devices and 2 replicas, then space equivalent to 2.5 of the devices will be available, and every block will be stored on two different devices. So contrary to this statement: "RAID10 provides a combination of RAID1 and RAID0, and is sometimes known as RAID1+0.", linux md raid10 is NOT raid1+0. Is something entirely new and different but unfortunately called raid10 perhaps due to it being able to create a raid1+0 array and a different layout using similar concepts. > > I read in context of raid10 about replicas of data (2 by default) and the > data layout (near/far/offset). I see in the output of mdadm -D the line > "Layout : near=2, far=1" and am not sure which layout is exactly used and > how it influences data layout/distribution in my case :| > > I would really appreciate a definite answer which partitions I can remove > and which I cannot remove at the same time because I need to perform some > disk maintenance tasks on this raid10 array. Thanks for all help! > If you want something that you can be sure about, do what I do. Make two raid1 md devices and then use them to make a raid0 device. raid10 is something cooked up by Neil Brown and but is not raid1+0. http://en.wikipedia.org/wiki/Linux_MD_RAID_10#LINUX-MD-RAID-10