我有一个 3 磁盘 RAID 5 阵列，我试图向其中添加第 4 个磁盘。
mdadm --add /dev/md6 /dev/sdb1
mdadm --grow --raid-devices=4 /dev/md6
此操作成功启动并持续进行，直至达到 51.1%
cat /proc/mdstat
Personalities : [linear] [raid0] [raid1] [raid10] [raid6] [raid5] [raid4] [multipath] [faulty]
md6 : active raid5 sda1[0] sdb1[5] sdf1[3] sde1[4]
3906764800 blocks super 1.2 level 5, 512k chunk, algorithm 2 [4/4] [UUUU]
[==========>..........] reshape = 51.1% (998533632/1953382400) finish=9046506.1min speed=1K/sec
bitmap: 0/15 pages [0KB], 65536KB chunk
它已经停留在相同的 998533632 位置好几天了。我尝试了几次重启，但没有任何进展。停止阵列或尝试启动其中的逻辑卷会挂起。更改最小/最大速度参数没有效果。当我重新启动并重新设置阵列时，显示的速度稳步下降到几乎为 0。
mdadm --assemble /dev/md6 --verbose --uuid 90c2b5c3:3bbfa0d7:a5efaeed:726c43e2
我还没有尝试过比重启更激烈的措施，以下是我目前能想到的尽可能多的信息。请告诉我我还能做什么。我很乐意更改内核、内核配置或任何其他需要获取更好信息的操作。
内核：4.4.3 mdadm 3.4
ps aux | grep md6
root 5041 99.9 0.0 0 0 ? R 07:10 761:58 [md6_raid5]
root 5042 0.0 0.0 0 0 ? D 07:10 0:00 [md6_reshape]
这是一致的。raid 组件上的 cpu 为 100%，但重塑组件上的 cpu 不是 100%。
mdadm --detail --verbose /dev/md6
/dev/md6:
Version : 1.2
Creation Time : Fri Aug 29 21:13:52 2014
Raid Level : raid5
Array Size : 3906764800 (3725.78 GiB 4000.53 GB)
Used Dev Size : 1953382400 (1862.89 GiB 2000.26 GB)
Raid Devices : 4
Total Devices : 4
Persistence : Superblock is persistent
Intent Bitmap : Internal
Update Time : Wed Apr 27 07:10:07 2016
State : clean, reshaping
Active Devices : 4
Working Devices : 4
Failed Devices : 0
Spare Devices : 0
Layout : left-symmetric
Chunk Size : 512K
Reshape Status : 51% complete
Delta Devices : 1, (3->4)
Name : Alpheus:6 (local to host Alpheus)
UUID : 90c2b5c3:3bbfa0d7:a5efaeed:726c43e2
Events : 47975
Number Major Minor RaidDevice State
0 8 1 0 active sync /dev/sda1
4 8 65 1 active sync /dev/sde1
3 8 81 2 active sync /dev/sdf1
5 8 17 3 active sync /dev/sdb1
查看单个磁盘时，我可以看到 MD6 成员上的活动较少。此活动往往与 /proc/mdstat 报告的总体速率相符
iostat
Linux 4.4.3-gentoo (Alpheus) 04/27/2016 _x86_64_ (4 CPU)
avg-cpu: %user %nice %system %iowait %steal %idle
1.84 0.00 24.50 0.09 0.00 73.57
Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn
sda 0.02 2.72 1.69 128570 79957
sdb 0.01 0.03 1.69 1447 79889
sdd 3.85 2.27 56.08 106928 2646042
sde 0.02 2.73 1.69 128610 79961
sdf 0.02 2.72 1.69 128128 79961
sdc 4.08 5.44 56.08 256899 2646042
md0 2.91 7.62 55.08 359714 2598725
dm-0 0.00 0.03 0.00 1212 0
dm-1 0.00 0.05 0.00 2151 9
dm-2 2.65 6.52 3.42 307646 161296
dm-3 0.19 1.03 51.66 48377 2437420
md6 0.00 0.02 0.00 1036 0
dmesg 看起来不错
dmesg
[ 1199.426995] md: bind<sde1>
[ 1199.427779] md: bind<sdf1>
[ 1199.428379] md: bind<sdb1>
[ 1199.428592] md: bind<sda1>
[ 1199.429260] md/raid:md6: reshape will continue
[ 1199.429274] md/raid:md6: device sda1 operational as raid disk 0
[ 1199.429275] md/raid:md6: device sdb1 operational as raid disk 3
[ 1199.429276] md/raid:md6: device sdf1 operational as raid disk 2
[ 1199.429277] md/raid:md6: device sde1 operational as raid disk 1
[ 1199.429498] md/raid:md6: allocated 4338kB
[ 1199.429807] md/raid:md6: raid level 5 active with 4 out of 4 devices, algorithm 2
[ 1199.429810] RAID conf printout:
[ 1199.429811] --- level:5 rd:4 wd:4
[ 1199.429812] disk 0, o:1, dev:sda1
[ 1199.429814] disk 1, o:1, dev:sde1
[ 1199.429816] disk 2, o:1, dev:sdf1
[ 1199.429817] disk 3, o:1, dev:sdb1
[ 1199.429993] created bitmap (15 pages) for device md6
[ 1199.430297] md6: bitmap initialized from disk: read 1 pages, set 0 of 29807 bits
[ 1199.474604] md6: detected capacity change from 0 to 4000527155200
[ 1199.474611] md: reshape of RAID array md6
[ 1199.474613] md: minimum _guaranteed_ speed: 1000 KB/sec/disk.
[ 1199.474614] md: using maximum available idle IO bandwidth (but not more than 200000 KB/sec) for reshape.
[ 1199.474617] md: using 128k window, over a total of 1953382400k.
lsblk 供参考
lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sda 8:0 0 1.8T 0 disk
└─sda1 8:1 0 1.8T 0 part
└─md6 9:6 0 3.7T 0 raid5
sdb 8:16 0 1.8T 0 disk
└─sdb1 8:17 0 1.8T 0 part
└─md6 9:6 0 3.7T 0 raid5
sdc 8:32 0 2.7T 0 disk
├─sdc1 8:33 0 16M 0 part
└─sdc2 8:34 0 2.7T 0 part
└─md0 9:0 0 2.7T 0 raid1
├─vg--mirror-swap 253:0 0 4G 0 lvm [SWAP]
├─vg--mirror-boot 253:1 0 256M 0 lvm /boot
├─vg--mirror-root 253:2 0 256G 0 lvm /
└─vg--mirror-data--mirror 253:3 0 2.5T 0 lvm /data/mirror
sdd 8:48 0 2.7T 0 disk
├─sdd1 8:49 0 16M 0 part
└─sdd2 8:50 0 2.7T 0 part
└─md0 9:0 0 2.7T 0 raid1
├─vg--mirror-swap 253:0 0 4G 0 lvm [SWAP]
├─vg--mirror-boot 253:1 0 256M 0 lvm /boot
├─vg--mirror-root 253:2 0 256G 0 lvm /
└─vg--mirror-data--mirror 253:3 0 2.5T 0 lvm /data/mirror
sde 8:64 0 1.8T 0 disk
└─sde1 8:65 0 1.8T 0 part
└─md6 9:6 0 3.7T 0 raid5
sdf 8:80 0 1.8T 0 disk
└─sdf1 8:81 0 1.8T 0 part
└─md6 9:6 0 3.7T 0 raid5
谢谢你的指点
答案1
几个小时后我偶然发现这博客文章中有一个（潜在的）解决方案，可以为我解决这个问题：
echo max > /sys/block/md0/md/sync_max
至于为什么？我不确定。我只是很高兴能找回一些冗余。