According to the manpage for mdadm, --write-mostly can only be used
add build, create, or add time. How does one set write-mostly devices
*after* they've been added?
mdadm /dev/mdX --write-mostly /dev/someDevice
succeeds but does nothing.
According to Documentation/md.txt, writing writemostly into
/sys/block/mdX/md/dev-someDevice/state
should do it, and it sort of appears to:
turnip:~ # mdadm --detail /dev/md11
/dev/md11:
Version : 01.00.03
Creation Time : Mon Dec 15 07:06:13 2008
Raid Level : raid1
Array Size : 78123988 (74.50 GiB 80.00 GB)
Used Dev Size : 156247976 (149.01 GiB 160.00 GB)
Raid Devices : 2
Total Devices : 2
Preferred Minor : 11
Persistence : Superblock is persistent
Intent Bitmap : Internal
Update Time : Mon Dec 15 12:21:20 2008
State : active
Active Devices : 2
Working Devices : 2
Failed Devices : 0
Spare Devices : 0
Name : turnip:11
UUID : cf24d099:9e174a79:2a2f6797:dcff1420
Events : 3840
Number Major Minor RaidDevice State
2 43 0 0 active sync /dev/nbd0
3 8 0 1 active sync /dev/sda
turnip:~ # echo writemostly > /sys/block/md11/md/dev-nbd0/state
turnip:~ # mdadm --detail /dev/md11
/dev/md11:
Version : 01.00.03
Creation Time : Mon Dec 15 07:06:13 2008
Raid Level : raid1
Array Size : 78123988 (74.50 GiB 80.00 GB)
Used Dev Size : 156247976 (149.01 GiB 160.00 GB)
Raid Devices : 2
Total Devices : 2
Preferred Minor : 11
Persistence : Superblock is persistent
Intent Bitmap : Internal
Update Time : Mon Dec 15 12:23:05 2008
State : active
Active Devices : 2
Working Devices : 2
Failed Devices : 0
Spare Devices : 0
Name : turnip:11
UUID : cf24d099:9e174a79:2a2f6797:dcff1420
Events : 3840
Number Major Minor RaidDevice State
2 43 0 0 active sync writemostly /dev/nbd0
3 8 0 1 active sync /dev/sda
turnip:~ # mdadm --examine-bitmap /dev/nbd0
Filename : /dev/nbd0
Magic : 6d746962
Version : 4
UUID : cf24d099:9e174a79:2a2f6797:dcff1420
Events : 3840
Events Cleared : 3840
State : OK
Chunksize : 4 MB
Daemon : 5s flush period
Write Mode : Normal
Sync Size : 78123988 (74.50 GiB 80.00 GB)
Bitmap : 19074 bits (chunks), 0 dirty (0.0%)
turnip:~ #
Why doesn't --examine-bitmap show the right mode?
Also, removing the bitmap from the array does not zero out the bitmap
on the actual device. Shouldn't it do that?
turnip:~ # mdadm --grow /dev/md11 --bitmap=none
turnip:~ # mdadm --examine-bitmap /dev/nbd0
Filename : /dev/nbd0
Magic : 6d746962
Version : 4
UUID : cf24d099:9e174a79:2a2f6797:dcff1420
Events : 3841
Events Cleared : 3841
State : OK
Chunksize : 4 MB
Daemon : 5s flush period
Write Mode : Normal
Sync Size : 78123988 (74.50 GiB 80.00 GB)
Bitmap : 19074 bits (chunks), 0 dirty (0.0%)
turnip:~ #
This is with mdadm 2.6.4 on 2.6.25.18-0.2-default
I can try mdadm 3.0 if you like.
--
Jon
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