G'day Neil,
Not a real problem, but a data point and possible issue.
I tried a hot replace on one of my main system disks. It all appeared to
work as-planned, but now I can't remove the replacement flag from /dev/sdg2.
I failed and removed /dev/sdg2 from /dev/md2, and then re-added it. It
synced up, a check shows no mismatches and it all appears to work ok,
but with the replacement flag set on that partition I can't do any
further hot-replace on that array. The flag survived a reboot.
I suspect I need to remove /dev/sdg2 and zero the superblock before
adding it back.
This came about when I originally replaced /dev/sds2 with /dev/sdg2. All
went well except at the end of the process sds2 was marked as failed and
sdg2 was marked as (R), and nothing I could do would change it. I could
remove sds2, but can't clear the replacement flag on sdg2.
I performed the original replacement on kernel 3.6.2, and am now running
3.6.6.
root@srv:/sys/block/md2/md# cat /proc/mdstat
<snip>
md2 : active raid10 sdg2[3](R) sdh2[2]
976247808 blocks super 1.2 512K chunks 2 far-copies [2/2] [UU]
bitmap: 1/8 pages [4KB], 65536KB chunk
root@srv:/sys/block/md2/md# mdadm --examine /dev/sd[hg]2
/dev/sdg2:
Magic : a92b4efc
Version : 1.2
Feature Map : 0x11
Array UUID : 6df98448:8cfbee7e:acdf3947:f282c441
Name : sysresccd:2
Creation Time : Sun May 8 14:02:40 2011
Raid Level : raid10
Raid Devices : 2
Avail Dev Size : 1952497072 (931.02 GiB 999.68 GB)
Array Size : 976247808 (931.02 GiB 999.68 GB)
Used Dev Size : 1952495616 (931.02 GiB 999.68 GB)
Data Offset : 2048 sectors
Super Offset : 8 sectors
State : clean
Device UUID : 9ba8a9af:e01c51d4:f9555d3e:2906f9a2
Internal Bitmap : 2 sectors from superblock
Update Time : Thu Nov 8 14:46:34 2012
Checksum : bb70195e - correct
Events : 1252869
Layout : far=2
Chunk Size : 512K
Device Role : Replacement device 1
Array State : AA ('A' == active, '.' == missing, 'R' == replacing)
/dev/sdh2:
Magic : a92b4efc
Version : 1.2
Feature Map : 0x1
Array UUID : 6df98448:8cfbee7e:acdf3947:f282c441
Name : sysresccd:2
Creation Time : Sun May 8 14:02:40 2011
Raid Level : raid10
Raid Devices : 2
Avail Dev Size : 1952497072 (931.02 GiB 999.68 GB)
Array Size : 976247808 (931.02 GiB 999.68 GB)
Used Dev Size : 1952495616 (931.02 GiB 999.68 GB)
Data Offset : 2048 sectors
Super Offset : 8 sectors
State : clean
Device UUID : 9245b92c:1b491bd5:0f35fb14:9faab3c9
Internal Bitmap : 2 sectors from superblock
Update Time : Thu Nov 8 14:46:34 2012
Checksum : 36a2660b - correct
Events : 1252869
Layout : far=2
Chunk Size : 512K
Device Role : Active device 0
Array State : AA ('A' == active, '.' == missing, 'R' == replacing)
root@srv:/sys/block/md2/md# mdadm --detail /dev/md2
/dev/md2:
Version : 1.2
Creation Time : Sun May 8 14:02:40 2011
Raid Level : raid10
Array Size : 976247808 (931.02 GiB 999.68 GB)
Used Dev Size : 976247808 (931.02 GiB 999.68 GB)
Raid Devices : 2
Total Devices : 2
Persistence : Superblock is persistent
Intent Bitmap : Internal
Update Time : Thu Nov 8 14:46:46 2012
State : active
Active Devices : 2
Working Devices : 2
Failed Devices : 0
Spare Devices : 0
Layout : far=2
Chunk Size : 512K
Name : sysresccd:2
UUID : 6df98448:8cfbee7e:acdf3947:f282c441
Events : 1252869
Number Major Minor RaidDevice State
2 8 114 0 active sync /dev/sdh2
3 8 98 1 active sync /dev/sdg2
root@srv:/sys/block/md2/md# cat dev-sdg2/state
in_sync,replacement
root@srv:/sys/block/md2/md# echo -replacement > dev-sdg2/state
bash: echo: write error: Device or resource busy
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