On 9/10/18 6:25 PM, Andreas Klauer wrote: > On Sun, Sep 09, 2018 at 03:32:47PM +0100, Wilson Jonathan wrote: >> Basically >> <-------- raid 0 ---------> >> <- raid 1 -> <- raid 1 -> >> M1 M1 M1 M2 M2 M2 >> >> If mdadm can't create the raid 10, with two three way mirrors > > Well, according to the manpage: > > Finally, the layout options for RAID10 are one of 'n', 'o' or 'f' > followed by a small number. The default is 'n2'. The supported > options are: > > 'n' signals 'near' copies. Multiple copies of one data block > are at similar offsets in different devices. > > The number is the number of copies of each datablock. 2 is normal, > 3 can be useful. > > So in theory, raid10 with --layout=n3 and six drives should be it. > Three copies of each data block in a single RAID, as requested. > > In practise it seems few people use this option. This is my preferred raid setup for anything not large media files. Linux MD raid10,n3. The number of disks does *not* have to be a multiple of 3, unlike raid 0+1 or raid 1+0 in a triple copy case. For example, with seven disks, the chunks would lay out like so: <---------- raid10,n3 -----------> <D1> <D2> <D3> <D4> <D5> <D6> <D7> A A A B B B C C C D D D E E E F F F G G G Phil
