On 13/12/17 03:57, Amy Chiang wrote: > my question is, > 1. "mdadm --grow /dev/md0 --level=6 --layout=preserve" will this > command create Q even though it degrades the array? > 2. Is backup happening in second step (reshaping)? if it's happening, > why don't I need a backup file? mdadm normally does not need a backup file. I don't know what --layout=preserve is doing, but the reshape always happens as an independent step, even if everything is specified at once. If the space is available (and mdadm by default always reserves spare space if it is given enough - I think a 2GB array will trigger a reserve allocation) a reshape always starts writing in the reserved space. It will lock and read stripe 1, and write it to reserved space. It will then lock and read stripe 2, stripe 3 etc until it runs out of reserved space. It will then use a window to make the new stripes active, unlock them, and then reserve the space those stripes used to occupy for the next bit of the reshape. So, at all times, the bit of the array being reshaped is locked and has multiple copies, and there's a window setting telling the management layer where to find the active bits of the array. Backup files are prone to cause trouble for novices, and this means they are not necessary. Great news. 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
