Re: Incorrect in-kernel bitmap on raid10

Mario 'BitKoenig' Holbe
2009-05-02T19:52:59Z

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On Sat, May 02, 2009 at 07:36:45AM +1000, NeilBrown wrote:
> On Sat, May 2, 2009 3:55 am, Mario 'BitKoenig' Holbe wrote:
> > However, can you confirm that the bitmap is really used in raid10
> > resync? I removed half of the disks (a correctly removable subset, of
...
> > I'll try to watch this and will trigger you again when I have more
> > stable evidence, but perhaps you have some faster test-cases, I have to
> 1/ it processes the whole array from start to finish in chunk-sized blocks
> and simply doesn't generate IO where it isn't needed. This is different

It definitely does generate I/O all the time here.

> 2/ With raid1, when it skips a whole bitmap chunk, that chunk is not
> included in the speed calculation. With raid10, everything is included.

It doesn't seem to touch the sync-limits here.

> 3/ I found a bug. If you have two devices missing and add just one,
> then after the recovery it might clear the bitmap even though
> there is another missing device. When that device is re-added, it will

The resync does never seem to respect the bitmap here.

> What speed are (were) you getting for resync. If it was around 200M/sec,
> then point 2 would explain it. If it was closer to the device speed,
> then there must be something else going wrong.

I guess, there is something else going wrong here. I attached a (quite
large, sorry for that) transcript of what I was doing with the output of
what I think could help.

What I did:
* I had a stable and clean raid10 out of 6 disks with superblocks all
uptodate, on-disk bitmaps all uptodate.
* I failed and removed 3 of the disks.
* I set some bits in the bitmap via mounting/umounting the raid10.
* I stopped the raid10 just to make sure all superblocks/bitmaps are
uptodate.
* I assembled the raid10 again with 3 out of 6 devices now.
* I re-added the 3 missing disks.
Please note, that I cannot add them all at the same time because if
the array is read-write the resync starts immediately when the first
device is added, while I cannot add devices as long as the array is
read-only.
In this immediately starting re-sync only the first of the three
spares is synched, it seems to ignore the bitmap, and it generates
I/O all the time, I just forgot to c'n'p the evidence. I have seen
that 3 times now with iostat, it really does I/O.
* I stopped and started the array to make it resync over all 3 spares
concurrently, it seems to ignore the bitmap, and it generates I/O
all the time again.

regards
Mario
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root@darkside:~# head -4 /proc/mdstat
Personalities : [raid1] [raid10]
md7 : active raid10 sdc1[0] sdf1[1] sdg1[3] sdh1[5] sde1[4] sdd1[2]
4395406848 blocks 512K chunks 2 near-copies [6/6] [UUUUUU]
bitmap: 0/131 pages [0KB], 16384KB chunk
root@darkside:~# mdadm -E /dev/sd[c-h]1
/dev/sdc1:
Magic : a92b4efc
Version : 0.90.00
UUID : bbcc5f03:13105928:bea48659:c10950ee
Creation Time : Sat Apr 18 18:26:28 2009
Raid Level : raid10
Used Dev Size : 1465135616 (1397.26 GiB 1500.30 GB)
Array Size : 4395406848 (4191.79 GiB 4500.90 GB)
Raid Devices : 6
Total Devices : 6
Preferred Minor : 7

Update Time : Sat May 2 21:22:22 2009
State : clean
Internal Bitmap : present
Active Devices : 6
Working Devices : 6
Failed Devices : 0
Spare Devices : 0
Checksum : e2f919ac - correct
Events : 13278

Layout : near=2
Chunk Size : 512K

Number Major Minor RaidDevice State
this 0 8 33 0 active sync /dev/sdc1

0 0 8 33 0 active sync /dev/sdc1
1 1 8 81 1 active sync /dev/sdf1
2 2 8 49 2 active sync /dev/sdd1
3 3 8 97 3 active sync /dev/sdg1
4 4 8 65 4 active sync /dev/sde1
5 5 8 113 5 active sync /dev/sdh1
/dev/sdd1:
Magic : a92b4efc
Version : 0.90.00
UUID : bbcc5f03:13105928:bea48659:c10950ee
Creation Time : Sat Apr 18 18:26:28 2009
Raid Level : raid10
Used Dev Size : 1465135616 (1397.26 GiB 1500.30 GB)
Array Size : 4395406848 (4191.79 GiB 4500.90 GB)
Raid Devices : 6
Total Devices : 6
Preferred Minor : 7

Update Time : Sat May 2 21:22:22 2009
State : clean
Internal Bitmap : present
Active Devices : 6
Working Devices : 6
Failed Devices : 0
Spare Devices : 0
Checksum : e2f919c0 - correct
Events : 13278

Layout : near=2
Chunk Size : 512K

Number Major Minor RaidDevice State
this 2 8 49 2 active sync /dev/sdd1

0 0 8 33 0 active sync /dev/sdc1
1 1 8 81 1 active sync /dev/sdf1
2 2 8 49 2 active sync /dev/sdd1
3 3 8 97 3 active sync /dev/sdg1
4 4 8 65 4 active sync /dev/sde1
5 5 8 113 5 active sync /dev/sdh1
/dev/sde1:
Magic : a92b4efc
Version : 0.90.00
UUID : bbcc5f03:13105928:bea48659:c10950ee
Creation Time : Sat Apr 18 18:26:28 2009
Raid Level : raid10
Used Dev Size : 1465135616 (1397.26 GiB 1500.30 GB)
Array Size : 4395406848 (4191.79 GiB 4500.90 GB)
Raid Devices : 6
Total Devices : 6
Preferred Minor : 7

Update Time : Sat May 2 21:22:22 2009
State : clean
Internal Bitmap : present
Active Devices : 6
Working Devices : 6
Failed Devices : 0
Spare Devices : 0
Checksum : e2f919d4 - correct
Events : 13278

Layout : near=2
Chunk Size : 512K

Number Major Minor RaidDevice State
this 4 8 65 4 active sync /dev/sde1

0 0 8 33 0 active sync /dev/sdc1
1 1 8 81 1 active sync /dev/sdf1
2 2 8 49 2 active sync /dev/sdd1
3 3 8 97 3 active sync /dev/sdg1
4 4 8 65 4 active sync /dev/sde1
5 5 8 113 5 active sync /dev/sdh1
/dev/sdf1:
Magic : a92b4efc
Version : 0.90.00
UUID : bbcc5f03:13105928:bea48659:c10950ee
Creation Time : Sat Apr 18 18:26:28 2009
Raid Level : raid10
Used Dev Size : 1465135616 (1397.26 GiB 1500.30 GB)
Array Size : 4395406848 (4191.79 GiB 4500.90 GB)
Raid Devices : 6
Total Devices : 6
Preferred Minor : 7

Update Time : Sat May 2 21:22:22 2009
State : clean
Internal Bitmap : present
Active Devices : 6
Working Devices : 6
Failed Devices : 0
Spare Devices : 0
Checksum : e2f919de - correct
Events : 13278

Layout : near=2
Chunk Size : 512K

Number Major Minor RaidDevice State
this 1 8 81 1 active sync /dev/sdf1

0 0 8 33 0 active sync /dev/sdc1
1 1 8 81 1 active sync /dev/sdf1
2 2 8 49 2 active sync /dev/sdd1
3 3 8 97 3 active sync /dev/sdg1
4 4 8 65 4 active sync /dev/sde1
5 5 8 113 5 active sync /dev/sdh1
/dev/sdg1:
Magic : a92b4efc
Version : 0.90.00
UUID : bbcc5f03:13105928:bea48659:c10950ee
Creation Time : Sat Apr 18 18:26:28 2009
Raid Level : raid10
Used Dev Size : 1465135616 (1397.26 GiB 1500.30 GB)
Array Size : 4395406848 (4191.79 GiB 4500.90 GB)
Raid Devices : 6
Total Devices : 6
Preferred Minor : 7

Update Time : Sat May 2 21:22:22 2009
State : clean
Internal Bitmap : present
Active Devices : 6
Working Devices : 6
Failed Devices : 0
Spare Devices : 0
Checksum : e2f919f2 - correct
Events : 13278

Layout : near=2
Chunk Size : 512K

Number Major Minor RaidDevice State
this 3 8 97 3 active sync /dev/sdg1

0 0 8 33 0 active sync /dev/sdc1
1 1 8 81 1 active sync /dev/sdf1
2 2 8 49 2 active sync /dev/sdd1
3 3 8 97 3 active sync /dev/sdg1
4 4 8 65 4 active sync /dev/sde1
5 5 8 113 5 active sync /dev/sdh1
/dev/sdh1:
Magic : a92b4efc
Version : 0.90.00
UUID : bbcc5f03:13105928:bea48659:c10950ee
Creation Time : Sat Apr 18 18:26:28 2009
Raid Level : raid10
Used Dev Size : 1465135616 (1397.26 GiB 1500.30 GB)
Array Size : 4395406848 (4191.79 GiB 4500.90 GB)
Raid Devices : 6
Total Devices : 6
Preferred Minor : 7

Update Time : Sat May 2 21:22:22 2009
State : clean
Internal Bitmap : present
Active Devices : 6
Working Devices : 6
Failed Devices : 0
Spare Devices : 0
Checksum : e2f91a06 - correct
Events : 13278

Layout : near=2
Chunk Size : 512K

Number Major Minor RaidDevice State
this 5 8 113 5 active sync /dev/sdh1

0 0 8 33 0 active sync /dev/sdc1
1 1 8 81 1 active sync /dev/sdf1
2 2 8 49 2 active sync /dev/sdd1
3 3 8 97 3 active sync /dev/sdg1
4 4 8 65 4 active sync /dev/sde1
5 5 8 113 5 active sync /dev/sdh1
root@darkside:~# mdadm -X /dev/sd[c-h]1
Filename : /dev/sdc1
Magic : 6d746962
Version : 4
UUID : bbcc5f03:13105928:bea48659:c10950ee
Events : 13278
Events Cleared : 13278
State : OK
Chunksize : 16 MB
Daemon : 5s flush period
Write Mode : Normal
Sync Size : 4395406848 (4191.79 GiB 4500.90 GB)
Bitmap : 268275 bits (chunks), 0 dirty (0.0%)
Filename : /dev/sdd1
Magic : 6d746962
Version : 4
UUID : bbcc5f03:13105928:bea48659:c10950ee
Events : 13278
Events Cleared : 13278
State : OK
Chunksize : 16 MB
Daemon : 5s flush period
Write Mode : Normal
Sync Size : 4395406848 (4191.79 GiB 4500.90 GB)
Bitmap : 268275 bits (chunks), 0 dirty (0.0%)
Filename : /dev/sde1
Magic : 6d746962
Version : 4
UUID : bbcc5f03:13105928:bea48659:c10950ee
Events : 13278
Events Cleared : 13278
State : OK
Chunksize : 16 MB
Daemon : 5s flush period
Write Mode : Normal
Sync Size : 4395406848 (4191.79 GiB 4500.90 GB)
Bitmap : 268275 bits (chunks), 0 dirty (0.0%)
Filename : /dev/sdf1
Magic : 6d746962
Version : 4
UUID : bbcc5f03:13105928:bea48659:c10950ee
Events : 13278
Events Cleared : 13278
State : OK
Chunksize : 16 MB
Daemon : 5s flush period
Write Mode : Normal
Sync Size : 4395406848 (4191.79 GiB 4500.90 GB)
Bitmap : 268275 bits (chunks), 0 dirty (0.0%)
Filename : /dev/sdg1
Magic : 6d746962
Version : 4
UUID : bbcc5f03:13105928:bea48659:c10950ee
Events : 13278
Events Cleared : 13278
State : OK
Chunksize : 16 MB
Daemon : 5s flush period
Write Mode : Normal
Sync Size : 4395406848 (4191.79 GiB 4500.90 GB)
Bitmap : 268275 bits (chunks), 0 dirty (0.0%)
Filename : /dev/sdh1
Magic : 6d746962
Version : 4
UUID : bbcc5f03:13105928:bea48659:c10950ee
Events : 13278
Events Cleared : 13278
State : OK
Chunksize : 16 MB
Daemon : 5s flush period
Write Mode : Normal
Sync Size : 4395406848 (4191.79 GiB 4500.90 GB)
Bitmap : 268275 bits (chunks), 0 dirty (0.0%)
root@darkside:~# mdadm --fail /dev/md7 /dev/sd[fgh]1
mdadm: set /dev/sdf1 faulty in /dev/md7
mdadm: set /dev/sdg1 faulty in /dev/md7
mdadm: set /dev/sdh1 faulty in /dev/md7
root@darkside:~# mdadm --remove /dev/md7 /dev/sd[fgh]1
mdadm: hot removed /dev/sdf1
mdadm: hot removed /dev/sdg1
mdadm: hot removed /dev/sdh1
root@darkside:~# mount -a
root@darkside:~# umount /dev/md7
root@darkside:~# mdadm --stop /dev/md7
mdadm: stopped /dev/md7
root@darkside:~# mdadm -E /dev/sd[c-h]1
/dev/sdc1:
Magic : a92b4efc
Version : 0.90.00
UUID : bbcc5f03:13105928:bea48659:c10950ee
Creation Time : Sat Apr 18 18:26:28 2009
Raid Level : raid10
Used Dev Size : 1465135616 (1397.26 GiB 1500.30 GB)
Array Size : 4395406848 (4191.79 GiB 4500.90 GB)
Raid Devices : 6
Total Devices : 3
Preferred Minor : 7

Update Time : Sat May 2 21:24:31 2009
State : clean
Internal Bitmap : present
Active Devices : 3
Working Devices : 3
Failed Devices : 3
Spare Devices : 0
Checksum : e2f91915 - correct
Events : 13294

Layout : near=2
Chunk Size : 512K

Number Major Minor RaidDevice State
this 0 8 33 0 active sync /dev/sdc1

0 0 8 33 0 active sync /dev/sdc1
1 1 0 0 1 faulty removed
2 2 8 49 2 active sync /dev/sdd1
3 3 0 0 3 faulty removed
4 4 8 65 4 active sync /dev/sde1
5 5 0 0 5 faulty removed
/dev/sdd1:
Magic : a92b4efc
Version : 0.90.00
UUID : bbcc5f03:13105928:bea48659:c10950ee
Creation Time : Sat Apr 18 18:26:28 2009
Raid Level : raid10
Used Dev Size : 1465135616 (1397.26 GiB 1500.30 GB)
Array Size : 4395406848 (4191.79 GiB 4500.90 GB)
Raid Devices : 6
Total Devices : 3
Preferred Minor : 7

Update Time : Sat May 2 21:24:31 2009
State : clean
Internal Bitmap : present
Active Devices : 3
Working Devices : 3
Failed Devices : 3
Spare Devices : 0
Checksum : e2f91929 - correct
Events : 13294

Layout : near=2
Chunk Size : 512K

Number Major Minor RaidDevice State
this 2 8 49 2 active sync /dev/sdd1

0 0 8 33 0 active sync /dev/sdc1
1 1 0 0 1 faulty removed
2 2 8 49 2 active sync /dev/sdd1
3 3 0 0 3 faulty removed
4 4 8 65 4 active sync /dev/sde1
5 5 0 0 5 faulty removed
/dev/sde1:
Magic : a92b4efc
Version : 0.90.00
UUID : bbcc5f03:13105928:bea48659:c10950ee
Creation Time : Sat Apr 18 18:26:28 2009
Raid Level : raid10
Used Dev Size : 1465135616 (1397.26 GiB 1500.30 GB)
Array Size : 4395406848 (4191.79 GiB 4500.90 GB)
Raid Devices : 6
Total Devices : 3
Preferred Minor : 7

Update Time : Sat May 2 21:24:31 2009
State : clean
Internal Bitmap : present
Active Devices : 3
Working Devices : 3
Failed Devices : 3
Spare Devices : 0
Checksum : e2f9193d - correct
Events : 13294

Layout : near=2
Chunk Size : 512K

Number Major Minor RaidDevice State
this 4 8 65 4 active sync /dev/sde1

0 0 8 33 0 active sync /dev/sdc1
1 1 0 0 1 faulty removed
2 2 8 49 2 active sync /dev/sdd1
3 3 0 0 3 faulty removed
4 4 8 65 4 active sync /dev/sde1
5 5 0 0 5 faulty removed
/dev/sdf1:
Magic : a92b4efc
Version : 0.90.00
UUID : bbcc5f03:13105928:bea48659:c10950ee
Creation Time : Sat Apr 18 18:26:28 2009
Raid Level : raid10
Used Dev Size : 1465135616 (1397.26 GiB 1500.30 GB)
Array Size : 4395406848 (4191.79 GiB 4500.90 GB)
Raid Devices : 6
Total Devices : 6
Preferred Minor : 7

Update Time : Sat May 2 21:22:22 2009
State : clean
Internal Bitmap : present
Active Devices : 6
Working Devices : 6
Failed Devices : 0
Spare Devices : 0
Checksum : e2f919de - correct
Events : 13278

Layout : near=2
Chunk Size : 512K

Number Major Minor RaidDevice State
this 1 8 81 1 active sync /dev/sdf1

0 0 8 33 0 active sync /dev/sdc1
1 1 8 81 1 active sync /dev/sdf1
2 2 8 49 2 active sync /dev/sdd1
3 3 8 97 3 active sync /dev/sdg1
4 4 8 65 4 active sync /dev/sde1
5 5 8 113 5 active sync /dev/sdh1
/dev/sdg1:
Magic : a92b4efc
Version : 0.90.00
UUID : bbcc5f03:13105928:bea48659:c10950ee
Creation Time : Sat Apr 18 18:26:28 2009
Raid Level : raid10
Used Dev Size : 1465135616 (1397.26 GiB 1500.30 GB)
Array Size : 4395406848 (4191.79 GiB 4500.90 GB)
Raid Devices : 6
Total Devices : 6
Preferred Minor : 7

Update Time : Sat May 2 21:23:51 2009
State : clean
Internal Bitmap : present
Active Devices : 5
Working Devices : 5
Failed Devices : 1
Spare Devices : 0
Checksum : e2f91a5e - correct
Events : 13280

Layout : near=2
Chunk Size : 512K

Number Major Minor RaidDevice State
this 3 8 97 3 active sync /dev/sdg1

0 0 8 33 0 active sync /dev/sdc1
1 1 0 0 1 faulty removed
2 2 8 49 2 active sync /dev/sdd1
3 3 8 97 3 active sync /dev/sdg1
4 4 8 65 4 active sync /dev/sde1
5 5 8 113 5 active sync /dev/sdh1
/dev/sdh1:
Magic : a92b4efc
Version : 0.90.00
UUID : bbcc5f03:13105928:bea48659:c10950ee
Creation Time : Sat Apr 18 18:26:28 2009
Raid Level : raid10
Used Dev Size : 1465135616 (1397.26 GiB 1500.30 GB)
Array Size : 4395406848 (4191.79 GiB 4500.90 GB)
Raid Devices : 6
Total Devices : 6
Preferred Minor : 7

Update Time : Sat May 2 21:23:51 2009
State : clean
Internal Bitmap : present
Active Devices : 4
Working Devices : 4
Failed Devices : 2
Spare Devices : 0
Checksum : e2f91a87 - correct
Events : 13282

Layout : near=2
Chunk Size : 512K

Number Major Minor RaidDevice State
this 5 8 113 5 active sync /dev/sdh1

0 0 8 33 0 active sync /dev/sdc1
1 1 0 0 1 faulty removed
2 2 8 49 2 active sync /dev/sdd1
3 3 0 0 3 faulty removed
4 4 8 65 4 active sync /dev/sde1
5 5 8 113 5 active sync /dev/sdh1
root@darkside:~# mdadm -X /dev/sd[c-h]1
Filename : /dev/sdc1
Magic : 6d746962
Version : 4
UUID : bbcc5f03:13105928:bea48659:c10950ee
Events : 13294
Events Cleared : 13278
State : OK
Chunksize : 16 MB
Daemon : 5s flush period
Write Mode : Normal
Sync Size : 4395406848 (4191.79 GiB 4500.90 GB)
Bitmap : 268275 bits (chunks), 3 dirty (0.0%)
Filename : /dev/sdd1
Magic : 6d746962
Version : 4
UUID : bbcc5f03:13105928:bea48659:c10950ee
Events : 13294
Events Cleared : 13278
State : OK
Chunksize : 16 MB
Daemon : 5s flush period
Write Mode : Normal
Sync Size : 4395406848 (4191.79 GiB 4500.90 GB)
Bitmap : 268275 bits (chunks), 3 dirty (0.0%)
Filename : /dev/sde1
Magic : 6d746962
Version : 4
UUID : bbcc5f03:13105928:bea48659:c10950ee
Events : 13294
Events Cleared : 13278
State : OK
Chunksize : 16 MB
Daemon : 5s flush period
Write Mode : Normal
Sync Size : 4395406848 (4191.79 GiB 4500.90 GB)
Bitmap : 268275 bits (chunks), 3 dirty (0.0%)
Filename : /dev/sdf1
Magic : 6d746962
Version : 4
UUID : bbcc5f03:13105928:bea48659:c10950ee
Events : 13278
Events Cleared : 13278
State : OK
Chunksize : 16 MB
Daemon : 5s flush period
Write Mode : Normal
Sync Size : 4395406848 (4191.79 GiB 4500.90 GB)
Bitmap : 268275 bits (chunks), 0 dirty (0.0%)
Filename : /dev/sdg1
Magic : 6d746962
Version : 4
UUID : bbcc5f03:13105928:bea48659:c10950ee
Events : 13280
Events Cleared : 13278
State : OK
Chunksize : 16 MB
Daemon : 5s flush period
Write Mode : Normal
Sync Size : 4395406848 (4191.79 GiB 4500.90 GB)
Bitmap : 268275 bits (chunks), 0 dirty (0.0%)
Filename : /dev/sdh1
Magic : 6d746962
Version : 4
UUID : bbcc5f03:13105928:bea48659:c10950ee
Events : 13282
Events Cleared : 13278
State : OK
Chunksize : 16 MB
Daemon : 5s flush period
Write Mode : Normal
Sync Size : 4395406848 (4191.79 GiB 4500.90 GB)
Bitmap : 268275 bits (chunks), 0 dirty (0.0%)
root@darkside:~# mdadm -A /dev/md7
[115116.898904] md: bind<sdf1>
[115116.907579] md: bind<sdd1>
[115116.916526] md: bind<sdg1>
[115116.926345] md: bind<sde1>
[115116.935542] md: bind<sdh1>
[115116.944477] md: bind<sdc1>
[115116.953071] md: kicking non-fresh sdh1 from array!
[115116.967686] md: unbind<sdh1>
[115116.977298] md: export_rdev(sdh1)
[115116.987495] md: kicking non-fresh sdg1 from array!
[115117.002105] md: unbind<sdg1>
[115117.012009] md: export_rdev(sdg1)
[115117.022209] md: kicking non-fresh sdf1 from array!
[115117.036817] md: unbind<sdf1>
[115117.046827] md: export_rdev(sdf1)
[115117.058179] raid10: raid set md7 active with 3 out of 6 devices
[115117.083006] md7: bitmap initialized from disk: read 9/9 pages, set 3 bits
[115117.103594] created bitmap (131 pages) for device md7
[115117.171218] md7: detected capacity change from 0 to 4500896612352
[115117.189718] md7: unknown partition table
mdadm: /dev/md7 has been started with 3 drives (out of 6).
root@darkside:~# mdadm --readonly /dev/md7
[115125.143499] md: md7 switched to read-only mode.
root@darkside:~# mdadm --add /dev/md7 /dev/sd[fgh]1
mdadm: add new device failed for /dev/sdf1 as 6: Read-only file system
root@darkside:~# head -4 /proc/mdstat
Personalities : [raid1] [raid10]
md7 : active (read-only) raid10 sdc1[0] sde1[4] sdd1[2]
4395406848 blocks 512K chunks 2 near-copies [6/3] [U_U_U_]
bitmap: 2/131 pages [8KB], 16384KB chunk
root@darkside:~# mdadm --readwrite /dev/md7
[115207.027682] md: md7 switched to read-write mode.
root@darkside:~# mdadm --add /dev/md7 /dev/sd[fgh]1
[115218.558523] md: bind<sdf1>
[115218.641655] RAID10 conf printout:
[115218.651846] --- wd:3 rd:6
[115218.660217] disk 0, wo:0, o:1, dev:sdc1
[115218.660219] disk 1, wo:1, o:1, dev:sdf1
[115218.660220] disk 2, wo:0, o:1, dev:sdd1
[115218.660222] disk 4, wo:0, o:1, dev:sde1
[115218.709281] md: recovery of RAID array md7
[115218.721834] md: minimum _guaranteed_ speed: 1000 KB/sec/disk.
[115218.739591] md: using maximum available idle IO bandwidth (but not more than 200000 KB/sec) for recovery.
[115218.739596] md: using 128k window, over a total of 1465135616 blocks.
mdadm: re-added /dev/sdf1
[115220.582354] md: bind<sdg1>
[115221.844379] md: bind<sdh1>
mdadm: re-added /dev/sdg1
mdadm: re-added /dev/sdh1
root@darkside:~# head -4 /proc/mdstat
Personalities : [raid1] [raid10]
md7 : active raid10 sdh1[6](S) sdg1[7](S) sdf1[8] sdc1[0] sde1[4] sdd1[2]
4395406848 blocks 512K chunks 2 near-copies [6/3] [U_U_U_]
[>....................] recovery = 0.2% (3877760/1465135616) finish=200.9min speed=121180K/sec
root@darkside:~# sleep 60
root@darkside:~# head -4 /proc/mdstat
Personalities : [raid1] [raid10]
md7 : active raid10 sdh1[6](S) sdg1[7](S) sdf1[8] sdc1[0] sde1[4] sdd1[2]
4395406848 blocks 512K chunks 2 near-copies [6/3] [U_U_U_]
[>....................] recovery = 2.0% (29498240/1465135616) finish=193.0min speed=123907K/sec
root@darkside:~# mdadm --stop /dev/md7
mdadm: stopped /dev/md7
root@darkside:~# mdadm -A /dev/md7
mdadm: /dev/md7 has been started with 3 drives (out of 6) and 3 spares.
root@darkside:~# head -4 /proc/mdstat
Personalities : [raid1] [raid10]
md7 : active (auto-read-only) raid10 sdc1[0] sdf1[8](S) sdg1[7](S) sdh1[6](S) sde1[4] sdd1[2]
4395406848 blocks 512K chunks 2 near-copies [6/3] [U_U_U_]
bitmap: 1/131 pages [4KB], 16384KB chunk
root@darkside:~# mdadm --readwrite /dev/md7
root@darkside:~# head -4 /proc/mdstat
Personalities : [raid1] [raid10]
md7 : active raid10 sdc1[0] sdf1[8] sdg1[7] sdh1[6] sde1[4] sdd1[2]
4395406848 blocks 512K chunks 2 near-copies [6/3] [U_U_U_]
[>....................] recovery = 0.0% (172608/1465135616) finish=282.7min speed=86304K/sec
root@darkside:~# sleep 10
root@darkside:~# head -4 /proc/mdstat
Personalities : [raid1] [raid10]
md7 : active raid10 sdc1[0] sdf1[8] sdg1[7] sdh1[6] sde1[4] sdd1[2]
4395406848 blocks 512K chunks 2 near-copies [6/3] [U_U_U_]
[>....................] recovery = 0.2% (4008384/1465135616) finish=323.8min speed=75191K/sec
root@darkside:~# iostat -m /dev/sd[c-h] 10 2 | tail -11
avg-cpu: %user %nice %system %iowait %steal %idle
1,34 0,10 4,75 0,99 0,00 92,83

Device: tps MB_read/s MB_wrtn/s MB_read MB_wrtn
sdc 759,90 73,45 0,00 734 0
sdd 752,20 73,45 0,00 734 0
sde 753,10 73,45 0,00 734 0
sdf 730,70 0,00 73,45 0 734
sdg 261,10 0,00 73,47 0 734
sdh 290,60 0,00 73,41 0 734

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