- .devs_min = 2, + .devs_min = 1,
I think we should introduce another way how to determine the lower limit for the degraded mounts. We need the proper raidX constraints and use the degraded limits only if in case of the degraded mount.
.tolerated_failures = 1,
Which is exactly the tolerated_failures: degraded_devs_min == devs_min - tolerated_failures
that is devs_min is actually healthy_devs_min.
which works for all raid levels with redundancy.
But not for RAID5 and RAID6.
Here is a (simulation?) tool which gives some ready ans. I have added devs_min - tolerated_failures to it. https://github.com/asj/btrfs-raid-cal.git
I have copied the state table from the above repo and modified to add the above equation. [x1 = devs_increment * sub_stripes] [ndevs' = ndevs - ndevs % devs_increment] [num_stripes = ndevs' * dev_stripes] [data_stripes = num_stripes / ncopies] [missing_mirror_dev = x1 - ndevs'] [Y = devs_min - tolerated_failures ] R10 R1 DUP R0 Sn R5 R6 .sub_stripes = 2, 1, 1, 1, 1, 1, 1 .dev_stripes = 1, 1, 2, 1, 1, 1, 1 .devs_max = 0, 2, 1, 0, 1, 0, 0 .devs_min = 4, 1, 1, 2, 1, 2, 3 .tolerated_fails= 1, 1, 0, 0, 0, 1, 2 .devs_increment = 2, 2, 1, 1, 1, 1, 1 .ncopies = 2, 2, 2, 1, 1, 2, 3 x1 = 4, 2, 1, 1, 1, 1, 1 Y = 3, 0, 1, 2, 1, 1, 1 [ndevs = 9] ndevs = 9, 9, 9, 9, 9, 9, 9 ndevs' = 8, 2, 1, 9, 9, 9, 9 num_stripes = 8, 2, 2, 9, 1, 9, 9 data_stripes = 4, 1, 1, 9, 1, 8, 7 [ndevs = tolerated_fails + devs_min] ndevs = 5, 2, 1, 2, 1, 3, 5 ndevs' = 4, 2, 1, 2, 1, 3, 5 num_stripes = 4, 2, 2, 2, 1, 3, 5 data_stripes = 2, 1, 1, 2, 1, 1, 1 [ndevs = devs_min] ndevs = 3, 1, 1, 2, 1, 2, 3 ndevs' = 2, 0, 1, 2, 1, 2, 3 num_stripes = -, -, 2, 2, 1, 2, 3 data_stripes = -, -, 1, 2, 1, 1, 1 [ndevs = devs_min, with RAID1 patch fix] ndevs = 3, 1, 1, 2, 1, 2, 3 ndevs' = 3, 1, 1, 2, 1, 2, 3 num_stripes = 3, 1, 2, 2, 1, 2, 3 data_stripes = ?, 1, 1, 2, 1, 1, 1 > I am seeing problem as this: > RAID5&6 devs_min values are in the context of degraded volume. > RAID1&10.. devs_min values are in the context of healthy volume. > > RAID56 is correct. We already have devs_max to know the number > of devices in a healthy volumes. RAID1 is devs_min is wrong so > it ended up being same as devs_max. Thanks, Anand -- 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
