I have two software RAID volumes of differing speed and reliability on Ubuntu 12.10. I want to mirror the contents of the faster, but less reliable /dev/md0 to /dev/md1.
My plan was to build a composite RAID1 volume on top of /dev/md0 and /dev/md1 using mdadm, but I'm having trouble building the volume.
mdam warns that the individual component arrays appear to be part of an existing array, and after reboot the kenel states that the array is degraded and is in need of repair.
Is it possible to build a composite array of two existing software arrays? If not, is there some solution other than rsync that I'm overlooking? Bonus points if I can make the OS have a read preference for the faster /dev/md0.
command used to create arrays:
mdadm --create /dev/md0 --level=0 -c256 --raid-devices=4 /dev/xvdb /dev/xvdc /dev/xvdd /dev/xvde
mdadm --create /dev/md1 --level=10 -c256 --raid-devices=4 /dev/xvdf /dev/xvdg /dev/xvdh /dev/xvdi
mdadm --create /dev/md2 --level=1 -c256 --raid-devices=2 /dev/md0 /dev/md1
mdadm.conf:
DEVICE /dev/xvdb /dev/xvdc /dev/xvdd /dev/xvde
DEVICE /dev/xvdf /dev/xvdg /dev/xvdh /dev/xvdi
DEVICE /dev/md0 /dev/md1
ARRAY /dev/md0 metadata=1.2 name=dn1-c.foo.com:0 UUID=b6bf6a3f:09e60e75:a04ce9d6:8a668b84
ARRAY /dev/md1 metadata=1.2 name=dn1-c.foo.com:1 UUID=d02217aa:4188e959:2a5d07e9:28e0d724
ARRAY /dev/md2 metadata=1.2 name=dn1-c.foo.com:2 UUID=c5266085:2adcbd6d:de4a8335:87e255d6
relevent dmesg output:
[7333496.257635] md: bind<xvdd>
[7333496.262758] md: bind<xvdh>
[7333496.266326] md: bind<xvdc>
[7333496.270206] md: bind<xvdf>
[7333496.274588] md: bind<xvdb>
[7333496.279373] md: bind<xvdg>
[7333496.286136] md: bind<xvde>
[7333496.290990] bio: create slab <bio-1> at 1
[7333496.291006] md/raid0:md127: md_size is 3522926592 sectors.
[7333496.291012] md: RAID0 configuration for md127 - 1 zone
[7333496.291017] md: zone0=[xvdb/xvdc/xvdd/xvde]
[7333496.291026] zone-offset= 0KB, device-offset= 0KB, size=1761463296KB
[7333496.291033]
[7333496.291048] md127: detected capacity change from 0 to 1803738415104
[7333496.291154] md: bind<xvdi>
[7333496.294186] md127: unknown partition table
[7333496.296463] md: raid10 personality registered for level 10
[7333496.296830] md/raid10:md126: not clean -- starting background reconstruction
[7333496.296839] md/raid10:md126: active with 4 out of 4 devices
[7333496.296869] md126: detected capacity change from 0 to 2198754295808
[7333496.308765] raid6: int64x1 1748 MB/s
[7333496.314083] md126: unknown partition table
[7333496.376772] raid6: int64x2 2369 MB/s
[7333496.444782] raid6: int64x4 1634 MB/s
[7333496.512757] raid6: int64x8 1673 MB/s
[7333496.580754] raid6: sse2x1 4746 MB/s
[7333496.648749] raid6: sse2x2 5793 MB/s
[7333496.716755] raid6: sse2x4 6073 MB/s
[7333496.716766] raid6: using algorithm sse2x4 (6073 MB/s)
[7333496.717708] xor: automatically using best checksumming function: generic_sse
[7333496.736747] generic_sse: 2205.000 MB/sec
[7333496.736755] xor: using function: generic_sse (2205.000 MB/sec)
[7333496.738128] md: raid6 personality registered for level 6
[7333496.738138] md: raid5 personality registered for level 5
[7333496.738146] md: raid4 personality registered for level 4
contents of /dev:
root@dn1-c:/home/ubuntu# ls /dev/md*
/dev/md126 /dev/md127
/dev/md:
dn1-c.foo.com:0 dn1-c.foo.com:1
root@dn1-c:/home/ubuntu#
mdadm -D output
root@dn1-c:/home/ubuntu# mdadm -D /dev/md126
/dev/md126:
Version : 1.2
Creation Time : Wed Mar 13 16:29:17 2013
Raid Level : raid10
Array Size : 2147220992 (2047.75 GiB 2198.75 GB)
Used Dev Size : 1073610496 (1023.87 GiB 1099.38 GB)
Raid Devices : 4
Total Devices : 4
Persistence : Superblock is persistent
Update Time : Wed Mar 13 17:56:48 2013
State : clean, resyncing (PENDING)
Active Devices : 4
Working Devices : 4
Failed Devices : 0
Spare Devices : 0
Layout : near=2
Chunk Size : 256K
Name : dn1-c.foo.com:1 (local to host dn1-c.foo.com)
UUID : d02217aa:4188e959:2a5d07e9:28e0d724
Events : 5
Number Major Minor RaidDevice State
0 202 80 0 active sync /dev/xvdf
1 202 96 1 active sync /dev/xvdg
2 202 112 2 active sync /dev/xvdh
3 202 128 3 active sync /dev/xvdi
root@dn1-c:/home/ubuntu# mdadm -D /dev/md127
/dev/md127:
Version : 1.2
Creation Time : Wed Mar 13 16:28:23 2013
Raid Level : raid0
Array Size : 1761463296 (1679.86 GiB 1803.74 GB)
Raid Devices : 4
Total Devices : 4
Persistence : Superblock is persistent
Update Time : Wed Mar 13 16:28:23 2013
State : clean
Active Devices : 4
Working Devices : 4
Failed Devices : 0
Spare Devices : 0
Chunk Size : 256K
Name : dn1-c.foo.com:0 (local to host dn1-c.foo.com)
UUID : b6bf6a3f:09e60e75:a04ce9d6:8a668b84
Events : 0
Number Major Minor RaidDevice State
0 202 16 0 active sync /dev/xvdb
1 202 32 1 active sync /dev/xvdc
2 202 48 2 active sync /dev/xvdd
3 202 64 3 active sync /dev/xvde
