I think it might be time to replace one or both of my RAID 1 drives.
They have been giving good service for six years. Both still have good
smartctl reports but I am ready to move one out to be used as a member of
my backup solution using old drives to hold rsync backups. I would thus
give my RAID a fresh disk before there is an actual failure.
I recently experimented with adding a third partition to my swap raid
partition and that went very well, so I was thinking that this would
provide a safer method to replace one drive compared to failing it and
then replacing it.
My test makes me think it might be as easy as:
1. Partition new drive (plugged in via external SATA dock)
Use: fdisk /dev/sdc
2. Add 3rd partition to each RAID.
Use: mdadm /dev/md4 --grow --raid-devices=3 --add /dev/sdc2
3. Wait for all the resyncs.
Use: watch cat /proc/mdstat
4. Fail out sda for each RAID.
Use: mdadm /dev/md4 --fail /dev/sda2
5. Drop back down to two disk.
Use: mdadm /dev/md4 --grow --raid-devices=2
6. Make the old partitions "safe".
Use: mdadm --zero-superblock /dev/sdc2
7. Power down and swap sdc into sda slot.
I only tested that with version 1.2 metadata, so I would be interested if
there is anything above that would not work with version 0.90. Also note
that I did my test using my swap partition but it seems like the
procedure should not care what sort of partitioning is used.
Below is info about my setup and how I tested to come up with the above
steps...
I am:
15:40-doug@wombat-~>uname -a
Linux wombat.wombatz.com 4.2.3-200.fc22.x86_64 #1 SMP Thu Oct 8 03:23:55
UTC 2015 x86_64 x86_64 x86_64 GNU/Linux
15:40-doug@wombat-~>cat /etc/fedora-release
Fedora release 22 (Twenty Two)
15:40-doug@wombat-~>mdadm -V
mdadm - v3.3.2 - 21st August 2014
My RAID setup:
(I am not using RAID for /boot, instead I rsync /boot to /bootalt each
night. Otherwise everything is on RAID 1, including swap.)
15:23-doug@wombat-~/wombat-4/raid/current-2015-10-26>df -hT |grep -v
^tmpfs
Filesystem Type Size Used Avail Use% Mounted on
devtmpfs devtmpfs 4.4G 0 4.4G 0% /dev
/dev/md126 ext4 30G 11G 18G 39% /
/dev/sdb1 ext4 579M 126M 411M 24% /bootalt
/dev/md1 ext4 40G 18G 23G 44% /home
/dev/md123 ext4 422G 209G 192G 53% /data2
/dev/md125 ext4 422G 74G 327G 19% /data1
/dev/sda1 ext4 579M 126M 411M 24% /boot
15:09-doug@wombat-~>swapon -s
Filename Type Size Used
Priority
/dev/md4 partition 4946980 0 -1
(I am using UUID for /etc/mdadm.conf and in /etc/fstab so I did not
bother to "fix" the names when they got changed to md12x during Fedora
upgrades.)
15:19-doug@wombat-~>cat /proc/mdstat
Personalities : [raid1]
md123 : active raid1 sdb7[1] sda7[0]
448888128 blocks [2/2] [UU]
bitmap: 0/4 pages [0KB], 65536KB chunk
md125 : active raid1 sdb6[1] sda6[0]
448888128 blocks [2/2] [UU]
bitmap: 1/4 pages [4KB], 65536KB chunk
md1 : active raid1 sdb5[0] sda5[2]
41952620 blocks super 1.2 [2/2] [UU]
bitmap: 1/1 pages [4KB], 65536KB chunk
md126 : active raid1 sdb3[0] sda3[1]
31463232 blocks [2/2] [UU]
bitmap: 1/1 pages [4KB], 65536KB chunk
md4 : active raid1 sdb2[2] sda2[3]
4946984 blocks super 1.2 [2/2] [UU]
unused devices: <none>
Notes from the test I did using a partion on a older and smaller drive...
[root@wombat Documents]# mdadm --detail /dev/md4
/dev/md4:
Version : 1.2
Creation Time : Sat Mar 24 16:53:28 2012
Raid Level : raid1
Array Size : 4946984 (4.72 GiB 5.07 GB)
Used Dev Size : 4946984 (4.72 GiB 5.07 GB)
Raid Devices : 2
Total Devices : 2
Persistence : Superblock is persistent
Update Time : Fri Oct 23 10:55:06 2015
State : clean
Active Devices : 2
Working Devices : 2
Failed Devices : 0
Spare Devices : 0
Name : wombat.wombatz.com:4 (local to host wombat.wombatz.com)
UUID : 2382da1b:c77c04c7:9e4f955c:9450c809
Events : 541
Number Major Minor RaidDevice State
3 8 2 0 active sync /dev/sda2
2 8 18 1 active sync /dev/sdb2
[root@wombat Documents]# fdisk /dev/sdc
[snip]
[root@wombat doug]# mdadm /dev/md4 --grow --raid-devices=3 --add /dev/sdc2
mdadm: added /dev/sdc2
unfreeze
[root@wombat Documents]# cat /proc/mdstat
[snip]
md4 : active raid1 sdc2[4] sdb2[2] sda2[3]
4946984 blocks super 1.2 [3/2] [UU_]
[=======>.............] recovery = 39.2% (1941056/4946984)
finish=0.6min speed=71890K/sec
Soon it showed:
md4 : active raid1 sdc2[4] sdb2[2] sda2[3]
4946984 blocks super 1.2 [3/3] [UUU]
And now:
[root@wombat Documents]# mdadm --detail /dev/md4
/dev/md4:
Version : 1.2
Creation Time : Sat Mar 24 16:53:28 2012
Raid Level : raid1
Array Size : 4946984 (4.72 GiB 5.07 GB)
Used Dev Size : 4946984 (4.72 GiB 5.07 GB)
Raid Devices : 3
Total Devices : 3
Persistence : Superblock is persistent
Update Time : Sat Oct 24 12:57:39 2015
State : clean
Active Devices : 3
Working Devices : 3
Failed Devices : 0
Spare Devices : 0
Name : wombat.wombatz.com:4 (local to host wombat.wombatz.com)
UUID : 2382da1b:c77c04c7:9e4f955c:9450c809
Events : 562
Number Major Minor RaidDevice State
3 8 2 0 active sync /dev/sda2
2 8 18 1 active sync /dev/sdb2
4 8 33 2 active sync /dev/sdc2
Now try to remove it:
[root@wombat doug]# mdadm /dev/md4 --fail /dev/sdc2
mdadm: set /dev/sdc2 faulty in /dev/md4
[root@wombat doug]# mdadm /dev/md4 --grow --raid-devices=2
raid_disks for /dev/md4 set to 2
unfreeze
Seems good:
md4 : active raid1 sdc2[4](F) sdb2[2] sda2[3]
4946984 blocks super 1.2 [2/2] [UU]
Just to be safe:
mdadm --zero-superblock /dev/sdc2
--
Doug Herr
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