I'm trying to test a setup that I need in a couple of days.
a 3way mirrored RAID10, so i'm using a n3 layout.
i'm starting with just 3 disks, these 3 would be mirrored together, obviously:
sudo mdadm --create /dev/md0 --level=10 --layout=n3 --raid-devices=3
/dev/loop17 /dev/loop18 /dev/loop19
mdadm: Defaulting to version 1.2 metadata
mdadm: array /dev/md0 started.
$ sudo mdadm --detail /dev/md0
/dev/md0:
Version : 1.2
Creation Time : Sun Jan 12 09:13:37 2020
Raid Level : raid10
Array Size : 100352 (98.00 MiB 102.76 MB)
Used Dev Size : 100352 (98.00 MiB 102.76 MB)
Raid Devices : 3
Total Devices : 3
Persistence : Superblock is persistent
Update Time : Sun Jan 12 09:13:37 2020
State : clean
Active Devices : 3
Working Devices : 3
Failed Devices : 0
Spare Devices : 0
Layout : near=3
Chunk Size : 512K
Consistency Policy : resync
Name : ale-XPS13-9333:0 (local to host ale-XPS13-9333)
UUID : 5b0e8009:7df3ed1a:a56e9edb:aff8f7c3
Events : 17
Number Major Minor RaidDevice State
0 7 17 0 active sync set-A /dev/loop17
1 7 18 1 active sync set-B /dev/loop18
2 7 19 2 active sync set-C /dev/loop19
The array looks good to me, but why used dev size is equal to array size ?
In a 3way mirror it should be 3 times the array size.
Anyway, let's add 3 disks more:
$ sudo mdadm --add /dev/md0 /dev/loop20 /dev/loop21 /dev/loop22
mdadm: added /dev/loop20
mdadm: added /dev/loop21
mdadm: added /dev/loop22
$ sudo mdadm --grow /dev/md0 --raid-devices=6
$ sudo mdadm --detail /dev/md0
/dev/md0:
Version : 1.2
Creation Time : Sun Jan 12 09:13:37 2020
Raid Level : raid10
Array Size : 200704 (196.00 MiB 205.52 MB)
Used Dev Size : 100352 (98.00 MiB 102.76 MB)
Raid Devices : 6
Total Devices : 6
Persistence : Superblock is persistent
Update Time : Sun Jan 12 09:19:19 2020
State : clean, resyncing
Active Devices : 6
Working Devices : 6
Failed Devices : 0
Spare Devices : 0
Layout : near=3
Chunk Size : 512K
Consistency Policy : resync
Resync Status : 74% complete
Name : ale-XPS13-9333:0 (local to host ale-XPS13-9333)
UUID : 5b0e8009:7df3ed1a:a56e9edb:aff8f7c3
Events : 33
Number Major Minor RaidDevice State
0 7 17 0 active sync set-A /dev/loop17
1 7 18 1 active sync set-B /dev/loop18
2 7 19 2 active sync set-C /dev/loop19
5 7 22 3 active sync set-A /dev/loop22
4 7 21 4 active sync set-B /dev/loop21
3 7 20 5 active sync set-C /dev/loop20
Now array size is doubled, but used dev is still the same.
Is this normal ? Is this the right procedure to grow from a 3way
mirrors raid10 to a 3way mirrors raid10 with 6 disks ?
Other question: set-A, set-B, set-C means that disk on set-A is
replicated on set-B and set-C, right ? So I can't remove more than 2
disks (set-B and set-C, in example) but i can remove set-A from the
first line and set-B and set-C from the last two lines, as they are on
different mirrors.
Is possible to have a better output ? A RAID1+0 output is much easier
to understand, because I know that I can't remove multiple disks from
a single RAID1 subset.
