I have some performance issue with mdraid. I have one 18x10TB soft raid6 array that is resyncing at ~70MB/s:
kernel 5.8.13-1.el8
/dev/md0:
Version : 1.2
Creation Time : Mon Oct 5 15:11:15 2020
Raid Level : raid6
Array Size : 155136221184 (144.48 TiB 158.86 TB)
Used Dev Size : 9696013824 (9.03 TiB 9.93 TB)
Raid Devices : 18
Total Devices : 18
Persistence : Superblock is persistent
Intent Bitmap : Internal
Update Time : Wed Aug 18 18:35:42 2021
State : clean, degraded, resyncing
Active Devices : 17
Working Devices : 18
Failed Devices : 0
Spare Devices : 1
Layout : left-symmetric
Chunk Size : 512K
Consistency Policy : bitmap
Resync Status : 25% complete
Name : large2:0 (local to host large2)
UUID : bdb63778:b3765982:b257478b:70121351
Events : 500678
Number Major Minor RaidDevice State
18 8 5 0 active sync /dev/sda5
1 8 21 1 active sync /dev/sdb5
2 8 34 2 active sync /dev/sdc2
3 8 50 3 active sync /dev/sdd2
4 8 66 4 active sync /dev/sde2
5 8 82 5 active sync /dev/sdf2
- 0 0 6 removed
7 8 114 7 active sync /dev/sdh2
8 8 130 8 active sync /dev/sdi2
9 8 146 9 active sync /dev/sdj2
10 8 162 10 active sync /dev/sdk2
11 8 178 11 active sync /dev/sdl2
12 8 194 12 active sync /dev/sdm2
13 8 210 13 active sync /dev/sdn2
14 8 226 14 active sync /dev/sdo2
15 8 242 15 active sync /dev/sdp2
16 65 2 16 active sync /dev/sdq2
17 65 18 17 active sync /dev/sdr2
6 8 98 - spare /dev/sdg2
md0 : active raid6 sdg2[6](S) sda5[18] sdr2[17] sdq2[16] sdp2[15] sdo2[14] sdn2[13] sdm2[12] sdl2[11] sdk2[10] sdj2[9] sdi2[8] sdh2[7] sdf2[5] sde2[4] sdd2[3] sdc2[2] sdb5[1]
155136221184 blocks super 1.2 level 6, 512k chunk, algorithm 2 [18/17] [UUUUUU_UUUUUUUUUUU]
[=====>...............] resync = 25.0% (2431109212/9696013824) finish=1562.2min speed=77503K/sec
bitmap: 9/73 pages [36KB], 65536KB chunk
Device r/s w/s rkB/s wkB/s rrqm/s wrqm/s %rrqm %wrqm r_await w_await aqu-sz rareq-sz wareq-sz svctm %util
sdg 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
sdb 322.00 2.80 77282.40 6.60 16471.00 0.80 98.08 22.22 412.53 126.79 133.40 240.01 2.36 2.53 82.10
sdf 339.40 0.00 77758.40 0.00 16454.40 0.00 97.98 0.00 379.81 0.00 128.91 229.11 0.00 2.39 81.28
sdr 325.00 0.00 77414.40 0.00 16465.20 0.00 98.06 0.00 405.64 0.00 131.83 238.20 0.00 2.40 77.90
sdm 329.00 0.00 78477.60 0.00 16465.40 0.00 98.04 0.00 398.25 0.00 131.02 238.53 0.00 2.38 78.36
sdi 328.60 0.00 77084.00 0.00 16460.40 0.00 98.04 0.00 391.20 0.00 128.55 234.58 0.00 2.48 81.64
sdh 335.40 0.00 77753.60 0.00 16456.20 0.00 98.00 0.00 389.88 0.00 130.77 231.82 0.00 2.42 81.14
sdj 326.40 0.00 77700.80 0.00 16464.80 0.00 98.06 0.00 408.07 0.00 133.19 238.05 0.00 2.48 80.90
sde 328.60 0.00 77700.80 0.00 16462.60 0.00 98.04 0.00 398.74 0.00 131.03 236.46 0.00 2.46 80.92
sdn 332.00 0.00 77050.40 0.00 16456.60 0.00 98.02 0.00 382.56 0.00 127.01 232.08 0.00 2.35 78.12
sdl 324.80 0.00 76341.60 0.00 16461.20 0.00 98.07 0.00 385.14 0.00 125.09 235.04 0.00 2.40 78.00
sdp 326.60 0.00 76789.60 0.00 16461.00 0.00 98.05 0.00 393.01 0.00 128.36 235.12 0.00 2.38 77.76
sdq 325.00 0.00 77281.60 0.00 16464.60 0.00 98.06 0.00 404.60 0.00 131.49 237.79 0.00 2.40 77.94
sdk 331.80 0.00 77685.60 0.00 16459.40 0.00 98.02 0.00 386.56 0.00 128.26 234.13 0.00 2.34 77.48
sda 324.20 2.80 77067.20 6.60 16464.40 0.80 98.07 22.22 426.02 135.93 138.74 237.71 2.36 2.59 84.62
sdd 327.60 0.00 77276.00 0.00 16461.80 0.00 98.05 0.00 401.83 0.00 131.64 235.89 0.00 2.47 81.02
sdc 330.80 0.00 77605.60 0.00 16460.00 0.00 98.03 0.00 396.68 0.00 131.22 234.60 0.00 2.46 81.24
sdo 326.40 0.00 77927.20 0.00 16465.60 0.00 98.06 0.00 402.73 0.00 131.45 238.75 0.00 2.40 78.38
md0 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
.
and second 36x14TB soft raid6 that is doing initial resync at ~40MB/s:
.
kernel 5.13.11-1.el8
Version : 1.2
Creation Time : Tue Aug 17 09:37:39 2021
Raid Level : raid6
Array Size : 464838634496 (432.91 TiB 475.99 TB)
Used Dev Size : 13671724544 (12.73 TiB 14.00 TB)
Raid Devices : 36
Total Devices : 36
Persistence : Superblock is persistent
Intent Bitmap : Internal
Update Time : Wed Aug 18 16:39:11 2021
State : active, resyncing
Active Devices : 36
Working Devices : 36
Failed Devices : 0
Spare Devices : 0
Layout : left-symmetric
Chunk Size : 512K
Consistency Policy : bitmap
Resync Status : 32% complete
Name : large1:0 (local to host large1)
UUID : b7cace22:832e570f:eba39768:bb1a1ed6
Events : 20709
Number Major Minor RaidDevice State
0 8 33 0 active sync /dev/sdc1
1 8 49 1 active sync /dev/sdd1
2 8 65 2 active sync /dev/sde1
3 8 81 3 active sync /dev/sdf1
4 8 97 4 active sync /dev/sdg1
5 8 113 5 active sync /dev/sdh1
6 8 129 6 active sync /dev/sdi1
7 8 145 7 active sync /dev/sdj1
8 8 161 8 active sync /dev/sdk1
9 8 209 9 active sync /dev/sdn1
10 8 177 10 active sync /dev/sdl1
11 8 225 11 active sync /dev/sdo1
12 8 241 12 active sync /dev/sdp1
13 65 1 13 active sync /dev/sdq1
14 65 17 14 active sync /dev/sdr1
15 8 193 15 active sync /dev/sdm1
16 65 145 16 active sync /dev/sdz1
17 65 161 17 active sync /dev/sdaa1
18 65 33 18 active sync /dev/sds1
19 65 49 19 active sync /dev/sdt1
20 65 65 20 active sync /dev/sdu1
21 65 81 21 active sync /dev/sdv1
22 65 97 22 active sync /dev/sdw1
23 65 113 23 active sync /dev/sdx1
24 65 129 24 active sync /dev/sdy1
25 65 177 25 active sync /dev/sdab1
26 65 193 26 active sync /dev/sdac1
27 65 209 27 active sync /dev/sdad1
28 65 225 28 active sync /dev/sdae1
29 65 241 29 active sync /dev/sdaf1
30 66 1 30 active sync /dev/sdag1
31 66 17 31 active sync /dev/sdah1
32 66 33 32 active sync /dev/sdai1
33 66 49 33 active sync /dev/sdaj1
34 66 65 34 active sync /dev/sdak1
35 66 81 35 active sync /dev/sdal1
md0 : active raid6 sdal1[35] sdak1[34] sdaj1[33] sdah1[31] sdai1[32] sdag1[30] sdaf1[29] sdac1[26] sdae1[28] sdab1[25] sdad1[27] sds1[18] sdq1[13] sdz1[16] sdo1[11] sdp1[12] sdx1[23] sdr1[14] sdw1[22] sdn1[9] sdaa1[17] sdv1[21] sdu1[20] sdy1[24] sdt1[19] sdk1[8] sdm1[15] sdl1[10] sdh1[5] sdj1[7] sdf1[3] sdi1[6] sdc1[0] sdg1[4] sde1[2] sdd1[1]
464838634496 blocks super 1.2 level 6, 512k chunk, algorithm 2 [36/36] [UUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUU]
[======>..............] resync = 32.4% (4433869056/13671724544) finish=3954.9min speed=38929K/sec
bitmap: 70/102 pages [280KB], 65536KB chunk
Device r/s w/s rkB/s wkB/s rrqm/s wrqm/s %rrqm %wrqm r_await w_await aqu-sz rareq-sz wareq-sz svctm %util
sdc 9738.60 1.40 38956.00 5.80 0.40 0.40 0.00 22.22 0.20 9.29 1.93 4.00 4.14 0.07 71.82
sdd 9738.20 1.00 38952.80 2.60 0.00 0.00 0.00 0.00 0.89 5.80 8.68 4.00 2.60 0.07 71.60
sde 9738.60 1.40 38956.00 5.80 0.40 0.40 0.00 22.22 0.31 3.71 3.02 4.00 4.14 0.07 70.60
sdf 9738.40 1.00 38953.60 2.60 0.00 0.00 0.00 0.00 0.17 3.20 1.69 4.00 2.60 0.07 70.56
sdg 9738.40 1.00 38953.60 2.60 0.00 0.00 0.00 0.00 0.85 4.20 8.31 4.00 2.60 0.07 70.72
sdh 9738.40 1.00 38953.60 2.60 0.00 0.00 0.00 0.00 0.20 4.00 1.93 4.00 2.60 0.07 70.64
sdi 9738.60 1.00 38954.40 2.60 0.00 0.00 0.00 0.00 0.17 8.20 1.70 4.00 2.60 0.07 70.98
sdj 9714.60 1.00 38954.40 2.60 24.00 0.00 0.25 0.00 0.58 4.00 5.61 4.01 2.60 0.07 70.66
sdk 9677.00 1.00 38953.60 2.60 61.40 0.00 0.63 0.00 1.23 4.40 11.94 4.03 2.60 0.07 70.76
sdl 9738.40 1.00 38953.60 2.60 0.00 0.00 0.00 0.00 0.15 5.80 1.44 4.00 2.60 0.07 70.76
sdm 9738.40 1.00 38953.60 2.60 0.00 0.00 0.00 0.00 0.38 2.80 3.73 4.00 2.60 0.07 70.96
sdo 9705.60 1.00 38953.60 2.60 32.80 0.00 0.34 0.00 0.83 5.80 8.07 4.01 2.60 0.07 70.80
sdp 9738.40 1.00 38953.60 2.60 0.00 0.00 0.00 0.00 0.30 4.20 2.91 4.00 2.60 0.07 70.60
sdn 9738.40 1.00 38953.60 2.60 0.00 0.00 0.00 0.00 0.34 5.60 3.30 4.00 2.60 0.07 70.76
sdt 9659.80 1.00 38954.40 2.60 78.80 0.00 0.81 0.00 1.00 4.00 9.71 4.03 2.60 0.07 70.44
sds 9640.40 1.00 38954.40 2.60 98.20 0.00 1.01 0.00 1.29 5.60 12.42 4.04 2.60 0.07 70.60
sdq 9738.40 1.00 38953.60 2.60 0.00 0.00 0.00 0.00 0.30 4.40 2.92 4.00 2.60 0.07 70.68
sdu 9738.60 1.00 38954.40 2.60 0.00 0.00 0.00 0.00 0.13 4.40 1.31 4.00 2.60 0.07 70.66
sdv 9696.20 1.00 38954.40 2.60 42.40 0.00 0.44 0.00 1.30 4.20 12.57 4.02 2.60 0.07 70.76
sdw 9738.40 1.00 38953.60 2.60 0.00 0.00 0.00 0.00 0.94 4.20 9.13 4.00 2.60 0.07 70.70
sdy 9738.40 1.00 38953.60 2.60 0.00 0.00 0.00 0.00 0.11 4.40 1.05 4.00 2.60 0.07 70.62
sdr 9730.80 1.00 38953.60 2.60 7.60 0.00 0.08 0.00 1.22 4.20 11.87 4.00 2.60 0.07 70.68
sdx 9718.00 1.00 38954.40 2.60 20.60 0.00 0.21 0.00 0.88 4.20 8.57 4.01 2.60 0.07 70.70
sdaa 9738.40 1.00 38953.60 2.60 0.00 0.00 0.00 0.00 0.24 4.20 2.38 4.00 2.60 0.07 70.60
sdz 9738.40 1.00 38953.60 2.60 0.00 0.00 0.00 0.00 0.20 4.20 1.91 4.00 2.60 0.07 70.60
sdab 9633.60 1.00 38953.60 2.60 104.80 0.00 1.08 0.00 1.38 4.20 13.33 4.04 2.60 0.07 70.52
sdac 9639.20 1.00 38954.40 2.60 99.40 0.00 1.02 0.00 1.08 5.60 10.45 4.04 2.60 0.07 70.56
sdad 9536.20 1.00 38954.40 2.60 202.40 0.00 2.08 0.00 2.73 4.00 26.04 4.08 2.60 0.07 70.36
sdaf 9738.60 1.00 38954.40 2.60 0.00 0.00 0.00 0.00 0.37 4.00 3.63 4.00 2.60 0.07 70.64
sdae 9738.60 1.00 38954.40 2.60 0.00 0.00 0.00 0.00 0.16 5.40 1.61 4.00 2.60 0.07 70.72
sdag 9735.20 1.00 38940.80 2.60 0.00 0.00 0.00 0.00 0.46 5.80 4.48 4.00 2.60 0.07 70.76
sdai 9738.60 1.00 38954.40 2.60 0.00 0.00 0.00 0.00 0.31 4.00 3.01 4.00 2.60 0.07 70.60
sdah 9661.60 1.00 38955.20 2.60 77.00 0.00 0.79 0.00 1.51 4.20 14.57 4.03 2.60 0.07 70.70
sdal 9739.20 1.40 38958.40 5.80 0.40 0.40 0.00 22.22 0.27 4.86 2.65 4.00 4.14 0.07 70.80
sdaj 9738.60 1.00 38954.40 2.60 0.00 0.00 0.00 0.00 0.17 4.40 1.68 4.00 2.60 0.07 70.64
sdak 9738.80 1.00 38955.20 2.60 0.00 0.00 0.00 0.00 0.53 5.40 5.21 4.00 2.60 0.07 70.80
Both arrays are running on systems with 32+ cores, 64GB RAM+ with no other load.
Both arrays have stripe_cache_size = 32768.
md0_raid6 process is using 50-75% cpu in both servers.
Each drive in both arrays has >100MB/s sequential read when tested by fio.
10TB hdds is 18 drives array are: TOSHIBA MG06ACA10TE
# blockdev --report
RO RA SSZ BSZ StartSec Size Device
rw 8192 512 4096 0 10000831348736 /dev/sdg
rw 8192 512 4096 2048 1048576 /dev/sdg1
rw 8192 512 512 4096 10000829234688 /dev/sdg2
rw 8192 512 4096 0 10000831348736 /dev/sdb
rw 8192 512 4096 2048 1048576 /dev/sdb1
rw 8192 512 4096 4096 17179869184 /dev/sdb2
rw 8192 512 4096 33558528 1074790400 /dev/sdb3
rw 8192 512 4096 35657728 53720645632 /dev/sdb4
rw 8192 512 512 140580864 9928853929472 /dev/sdb5
rw 8192 512 4096 0 10000831348736 /dev/sdf
rw 8192 512 4096 2048 1048576 /dev/sdf1
rw 8192 512 512 4096 10000829234688 /dev/sdf2
rw 8192 512 4096 0 10000831348736 /dev/sdr
rw 8192 512 4096 2048 1048576 /dev/sdr1
rw 8192 512 512 4096 10000829234688 /dev/sdr2
rw 8192 512 4096 0 10000831348736 /dev/sdm
rw 8192 512 4096 2048 1048576 /dev/sdm1
rw 8192 512 512 4096 10000829234688 /dev/sdm2
rw 8192 512 4096 0 10000831348736 /dev/sdi
rw 8192 512 4096 2048 1048576 /dev/sdi1
rw 8192 512 512 4096 10000829234688 /dev/sdi2
rw 8192 512 4096 0 10000831348736 /dev/sdh
rw 8192 512 4096 2048 1048576 /dev/sdh1
rw 8192 512 512 4096 10000829234688 /dev/sdh2
rw 8192 512 4096 0 10000831348736 /dev/sdj
rw 8192 512 4096 2048 1048576 /dev/sdj1
rw 8192 512 512 4096 10000829234688 /dev/sdj2
rw 8192 512 4096 0 10000831348736 /dev/sde
rw 8192 512 4096 2048 1048576 /dev/sde1
rw 8192 512 512 4096 10000829234688 /dev/sde2
rw 8192 512 4096 0 10000831348736 /dev/sdn
rw 8192 512 4096 2048 1048576 /dev/sdn1
rw 8192 512 512 4096 10000829234688 /dev/sdn2
rw 8192 512 4096 0 10000831348736 /dev/sdl
rw 8192 512 4096 2048 1048576 /dev/sdl1
rw 8192 512 512 4096 10000829234688 /dev/sdl2
rw 8192 512 4096 0 10000831348736 /dev/sdp
rw 8192 512 4096 2048 1048576 /dev/sdp1
rw 8192 512 512 4096 10000829234688 /dev/sdp2
rw 8192 512 4096 0 10000831348736 /dev/sdq
rw 8192 512 4096 2048 1048576 /dev/sdq1
rw 8192 512 512 4096 10000829234688 /dev/sdq2
rw 8192 512 4096 0 10000831348736 /dev/sdk
rw 8192 512 4096 2048 1048576 /dev/sdk1
rw 8192 512 512 4096 10000829234688 /dev/sdk2
rw 8192 512 4096 0 10000831348736 /dev/sda
rw 8192 512 4096 2048 1048576 /dev/sda1
rw 8192 512 4096 4096 17179869184 /dev/sda2
rw 8192 512 4096 33558528 1074790400 /dev/sda3
rw 8192 512 4096 35657728 53720645632 /dev/sda4
rw 8192 512 512 140580864 9928853929472 /dev/sda5
rw 8192 512 4096 0 10000831348736 /dev/sdd
rw 8192 512 4096 2048 1048576 /dev/sdd1
rw 8192 512 512 4096 10000829234688 /dev/sdd2
rw 8192 512 4096 0 10000831348736 /dev/sdc
rw 8192 512 4096 2048 1048576 /dev/sdc1
rw 8192 512 512 4096 10000829234688 /dev/sdc2
rw 8192 512 4096 0 10000831348736 /dev/sdo
rw 8192 512 4096 2048 1048576 /dev/sdo1
rw 8192 512 512 4096 10000829234688 /dev/sdo2
rw 8192 512 4096 0 1072693248 /dev/md127
rw 8192 512 4096 0 53686042624 /dev/md126
rw 32768 512 4096 0 158859490492416 /dev/md0
14TB hdds in 36 drives array are: WDC WUH721414AL5201
# blockdev --report
RO RA SSZ BSZ StartSec Size Device
rw 8192 512 4096 0 480103981056 /dev/sda
rw 8192 512 4096 2048 535822336 /dev/sda1
rw 8192 512 4096 1048576 536870912 /dev/sda2
rw 8192 512 4096 2097152 447569985536 /dev/sda3
rw 8192 512 4096 876257280 31457280000 /dev/sda4
rw 8192 512 4096 0 480103981056 /dev/sdb
rw 8192 512 512 2048 535822336 /dev/sdb1
rw 8192 512 4096 1048576 536870912 /dev/sdb2
rw 8192 512 4096 2097152 447569985536 /dev/sdb3
rw 8192 512 4096 876257280 31457280000 /dev/sdb4
rw 8192 512 512 937698992 2080256 /dev/sdb5
rw 8192 512 4096 0 14000519643136 /dev/sdc
rw 8192 512 512 2048 13999981706752 /dev/sdc1
rw 8192 512 4096 0 14000519643136 /dev/sdd
rw 8192 512 512 2048 13999981706752 /dev/sdd1
rw 8192 512 4096 0 14000519643136 /dev/sde
rw 8192 512 512 2048 13999981706752 /dev/sde1
rw 8192 512 4096 0 14000519643136 /dev/sdf
rw 8192 512 512 2048 13999981706752 /dev/sdf1
rw 8192 512 4096 0 14000519643136 /dev/sdg
rw 8192 512 512 2048 13999981706752 /dev/sdg1
rw 8192 512 4096 0 14000519643136 /dev/sdh
rw 8192 512 512 2048 13999981706752 /dev/sdh1
rw 8192 512 4096 0 14000519643136 /dev/sdi
rw 8192 512 512 2048 13999981706752 /dev/sdi1
rw 8192 512 4096 0 14000519643136 /dev/sdj
rw 8192 512 512 2048 13999981706752 /dev/sdj1
rw 8192 512 4096 0 536281088 /dev/md2
rw 8192 512 4096 0 14000519643136 /dev/sdk
rw 8192 512 512 2048 13999981706752 /dev/sdk1
rw 8192 512 4096 0 14000519643136 /dev/sdl
rw 8192 512 512 2048 13999981706752 /dev/sdl1
rw 8192 512 4096 0 447435767808 /dev/md3
rw 8192 512 4096 0 14000519643136 /dev/sdm
rw 8192 512 512 2048 13999981706752 /dev/sdm1
rw 69632 512 4096 0 475994761723904 /dev/md0
rw 8192 512 4096 0 14000519643136 /dev/sdo
rw 8192 512 512 2048 13999981706752 /dev/sdo1
rw 8192 512 4096 0 14000519643136 /dev/sdp
rw 8192 512 512 2048 13999981706752 /dev/sdp1
rw 8192 512 4096 0 14000519643136 /dev/sdn
rw 8192 512 512 2048 13999981706752 /dev/sdn1
rw 8192 512 4096 0 14000519643136 /dev/sdt
rw 8192 512 512 2048 13999981706752 /dev/sdt1
rw 8192 512 4096 0 14000519643136 /dev/sds
rw 8192 512 512 2048 13999981706752 /dev/sds1
rw 8192 512 4096 0 14000519643136 /dev/sdq
rw 8192 512 512 2048 13999981706752 /dev/sdq1
rw 8192 512 4096 0 14000519643136 /dev/sdu
rw 8192 512 512 2048 13999981706752 /dev/sdu1
rw 8192 512 4096 0 14000519643136 /dev/sdv
rw 8192 512 512 2048 13999981706752 /dev/sdv1
rw 8192 512 4096 0 14000519643136 /dev/sdw
rw 8192 512 512 2048 13999981706752 /dev/sdw1
rw 8192 512 4096 0 14000519643136 /dev/sdy
rw 8192 512 512 2048 13999981706752 /dev/sdy1
rw 8192 512 4096 0 14000519643136 /dev/sdr
rw 8192 512 512 2048 13999981706752 /dev/sdr1
rw 8192 512 4096 0 14000519643136 /dev/sdx
rw 8192 512 512 2048 13999981706752 /dev/sdx1
rw 8192 512 4096 0 14000519643136 /dev/sdaa
rw 8192 512 512 2048 13999981706752 /dev/sdaa1
rw 8192 512 4096 0 14000519643136 /dev/sdz
rw 8192 512 512 2048 13999981706752 /dev/sdz1
rw 8192 512 4096 0 14000519643136 /dev/sdab
rw 8192 512 512 2048 13999981706752 /dev/sdab1
rw 8192 512 4096 0 14000519643136 /dev/sdac
rw 8192 512 512 2048 13999981706752 /dev/sdac1
rw 8192 512 4096 0 14000519643136 /dev/sdad
rw 8192 512 512 2048 13999981706752 /dev/sdad1
rw 8192 512 4096 0 14000519643136 /dev/sdaf
rw 8192 512 512 2048 13999981706752 /dev/sdaf1
rw 8192 512 4096 0 14000519643136 /dev/sdae
rw 8192 512 512 2048 13999981706752 /dev/sdae1
rw 8192 512 4096 0 14000519643136 /dev/sdag
rw 8192 512 512 2048 13999981706752 /dev/sdag1
rw 8192 512 4096 0 14000519643136 /dev/sdai
rw 8192 512 512 2048 13999981706752 /dev/sdai1
rw 8192 512 4096 0 14000519643136 /dev/sdah
rw 8192 512 512 2048 13999981706752 /dev/sdah1
rw 8192 512 4096 0 14000519643136 /dev/sdal
rw 8192 512 512 2048 13999981706752 /dev/sdal1
rw 8192 512 4096 0 14000519643136 /dev/sdaj
rw 8192 512 512 2048 13999981706752 /dev/sdaj1
rw 8192 512 4096 0 14000519643136 /dev/sdak
rw 8192 512 512 2048 13999981706752 /dev/sdak1
On both arrays sync_speed_min/sync_speed_max is set to 200000.
18drives array is connected as JBOD via LSI SAS3008 PCI-Express Fusion-MPT SAS-3
36 drives array is connected as JBOD via two controllers LSI SAS3008 PCI-Express Fusion-MPT SAS-3
All controllers are in PCI-E 3.0 x8 slots:
LnkSta: Speed 8GT/s (ok), Width x8 (ok)
My questions are:
- Why array with 36drives has almost two times slower resync rate ?
- iostat for array with 18 drives shows:
322.00 r/s
77282.40 rKB/s
16454.40 rrqm/s
but iostat for array with 36 drives shows:
9738.60 r/s
38956.00 rKB/s
0 rrqm/s
why second array is not doing io merge ?
- Is there anything i can try to speed up resync on second array ?
UPDATE
I was able to speed up 18drive array from 70MB/s to 180MB/s by increasing number of threads in mdraid:
echo 8 > /sys/block/md0/md/group_thread_cnt
what is even more intresting - doing the same on 36drive array resulted in decreasing performance from 40MB/s to 30MB/s.
UPDATE 2
Just noticed that rareq-sz from iostat on 36 drive array is only 4KB. It looks like all IO send to disks is always only 4KB. This is really strange. Why md raid is doing resync in 4KB chunks for this array ?
UPDATE 3
I have done a bit more research on 24 NVMe drives server and found
that resync speed bottleneck affect RAID6 with >16 drives:
# mdadm --create --verbose /dev/md0 --level=6 --raid-devices=16
/dev/nvme1n1 /dev/nvme2n1 /dev/nvme3n1 /dev/nvme4n1 /dev/nvme5n1
/dev/nvme6n1 /dev/nvme7n1 /dev/nvme8n1 /dev/nvme9n1 /dev/nvme10n1
/dev/nvme11n1 /dev/nvme12n1 /dev/nvme13n1 /dev/nvme14n1 /dev/nvme15n1
/dev/nvme16n1
# iostat -dx 5
Device r/s w/s rkB/s wkB/s rrqm/s wrqm/s
%rrqm %wrqm r_await w_await aqu-sz rareq-sz wareq-sz svctm %util
nvme0n1 0.00 0.00 0.00 0.00 0.00 0.00
0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
nvme1n1 342.60 0.40 161311.20 0.90 39996.60 0.00
99.15 0.00 2.88 0.00 0.99 470.84 2.25 2.51 86.04
nvme4n1 342.60 0.40 161311.20 0.90 39996.60 0.00
99.15 0.00 2.89 0.00 0.99 470.84 2.25 2.51 86.06
nvme5n1 342.60 0.40 161311.20 0.90 39996.60 0.00
99.15 0.00 2.89 0.00 0.99 470.84 2.25 2.51 86.14
nvme10n1 342.60 0.40 161311.20 0.90 39996.60 0.00
99.15 0.00 2.90 0.00 0.99 470.84 2.25 2.51 86.20
as you can see, there are 342 iops with ~470 rareq-sz, but when i
create RAID6 with 17 drives or more:
# mdadm --create --verbose /dev/md0 --level=6 --raid-devices=17
/dev/nvme1n1 /dev/nvme2n1 /dev/nvme3n1 /dev/nvme4n1 /dev/nvme5n1
/dev/nvme6n1 /dev/nvme7n1 /dev/nvme8n1 /dev/nvme9n1 /dev/nvme10n1
/dev/nvme11n1 /dev/nvme12n1 /dev/nvme13n1 /dev/nvme14n1 /dev/nvme15n1
/dev/nvme16n1 /dev/nvme17n1
# iostat -dx 5
Device r/s w/s rkB/s wkB/s rrqm/s wrqm/s
%rrqm %wrqm r_await w_await aqu-sz rareq-sz wareq-sz svctm %util
nvme0n1 0.00 0.00 0.00 0.00 0.00 0.00
0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
nvme1n1 21484.20 0.40 85936.80 0.90 0.00 0.00
0.00 0.00 0.04 0.00 0.82 4.00 2.25 0.05 99.16
nvme4n1 21484.00 0.40 85936.00 0.90 0.00 0.00
0.00 0.00 0.03 0.00 0.74 4.00 2.25 0.05 99.16
nvme5n1 21484.00 0.40 85936.00 0.90 0.00 0.00
0.00 0.00 0.04 0.00 0.84 4.00 2.25 0.05 99.16
rareq-sz drops to 4, iops increase to 21483 and resync speed drops to 85MB/s.
Why is it like that?
Could someone let me know which part of mdraid
kernel code is responsible for this limitation ?
