On 11/18/2017 09:52 PM, Goffredo Baroncelli wrote:
On 11/17/2017 01:36 PM, Anand Jain wrote:
If the device is not present at the time of (-o degrade) mount,
the mount context will create a dummy missing struct btrfs_device.
Later this device may reappear after the FS is mounted and
then device is included in the device list but it missed the
open_device part. So this patch handles that case by going
through the open_device steps which this device missed and finally
adds to the device alloc list.
What happens if the first devices got writes before the "last device" is joined ?
Supposing to have a raid1 pair of devices: sda, sdb
- sda is dissappeared (usb detached ?)
- the filesystem is mounted as
mount -o degraded /dev/sdb
- some writes happens on /dev/sdb
- the user reattach /dev/sda
- udev run "btrfs dev scan"
- the system joins /dev/sda to the filesystem disks pool
Because the filesystem is a raid1, btrfs may read from /dev/sdb (updated data) or /dev/sda (old data), or worse read something from the former and something from the later (metadata from sda and data from sdb ) ???
Thanks for the test scenario, this case is fine as its read from
the disk having highest generation number, so we pick sdb in the
case above.
Thanks, Anand
Am I missing something ?
BR
G.Baroncelli
--
To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
