I had someone wanting to take an existing disk full of data and expand it by adding a second disk. This seemed reasonable, and I thought of several ways you could do this, but none of them pan out: 1) Create a single disk raid0 using the existing disk, then reshape it adding the second disk. mdadm fails to add the second disk as a spare so that you can reshape, with the kernel complaining that personality does not support diskops. 2) Create a single disk raid1 using the existing disk, then reshape it adding the second disk. Apparently you can not reshape from raid1 to raid0. 3) Create a raid10 using the existing disk, setting the number of near copies to only 1 so as to preserve the existing data, then reshape adding the second disk. I ran into two problems here: a) mdadm refuses to create a single disk raid10, saying that at least two devices are needed for raid level 4 or 5. I am surprised that you can not create a single disk raid10 even with --force, and the message mentions the wrong level. I would think that a single disk raid10 with 2 far copies would be fairly useful. b) I tried 2 disks with one missing and mdadm refuses to create a raid10 with only a single near copy. The kernel complains that layout 0x101 is unsupported. Is there any way to accomplish this? -- 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
