On 02/01/18 03:49, Amy Chiang wrote: > I didn't specify --backup-file because I thought mdadm would give me a > warning if there's a possibility that I might lose my data if this > operation crash. I'm slightly surprised at your results (although I shouldn't be :-). Backup files are now almost entirely legacy - a modern setup should pretty much never need them - which is why I'm surprised at your results, I would have expected mdadm to ignore the backup-file option. In the old days, a reshape used to copy a stripe to backup, and then rewrite it. Rinse, lather and repeat. So the i/o overhead was high. Now, with "data offset" and superblock 1, mdadm calculates where the reshaped array is going to be, then starts copying from the old to array to where the new array does not overlap the old array. This makes a window where there are two copies of the data. When it runs out of space, it moves the window to create more space and carries on copying. As you can see, this is a lot less work ... Cheers, Wol -- 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
