I have grown a raid5 over the years with drives and resized partitions,
now I have upgraded to centos7 (from centos5). And I have the impression
the speed is not what it used to be.
Can this be because of some missalignment? How can this be verified?
If I monitor the individual disks with dstat it reads the raid drives at
very low speeds
dd if=/dev/md21 of=/dev/null bs=1M count=1500 iflag=direct
1500+0 records in
1500+0 records out
1572864000 bytes (1.6 GB) copied, 19.5879 s, 80.3 MB/s
0 0 : 0 0 : 0 0 : 0 0 : 0 0 : 0 0 :
0 0
0 0 : 0 0 : 0 0 : 0 0 : 0 0 : 0 0 :
0 0
0 0 : 0 0 : 0 0 : 0 0 : 0 0 : 0 0 :
0 0
256k 0 : 320k 0 : 320k 0 : 192k 0 : 256k 0 : 320k 0 :
256k 0
4672k 0 :4672k 0 :4672k 0 :4800k 0 :4672k 0 :4672k 0
:4736k 0
11M 0 : 11M 0 : 11M 0 : 11M 0 : 11M 0 : 11M 0 :
11M 0
10M 0 : 10M 0 : 10M 0 : 10M 0 : 10M 0 : 10M 0 :
10M 0
10M 0 : 10M 0 : 10M 0 : 10M 0 : 10M 0 : 10M 0 :
10M 0
13M 0 : 13M 0 : 13M 0 : 13M 0 : 13M 0 : 13M 0 :
13M 0
10M 0 : 10M 0 : 10M 0 : 10M 0 : 10M 0 : 10M 0 :
10M 0
11M 0 : 11M 0 : 11M 0 : 11M 0 : 11M 0 : 11M 0 :
11M 0
19M 0 : 19M 0 : 19M 0 : 19M 0 : 19M 0 : 19M 0 :
19M 0
9984k 0 :9792k 0 :9792k 0 :9792k 0 :9984k 0 :9984k 0
:9856k 0
13M 0 : 13M 0 : 13M 0 : 13M 0 : 13M 0 : 13M 0 :
13M 0
11M 0 : 11M 0 : 11M 0 : 11M 0 : 11M 0 : 11M 0 :
11M 0
12M 0 : 12M 0 : 12M 0 : 12M 0 : 12M 0 : 12M 0 :
12M 0
7872k 0 :7744k 0 :7808k 0 :7744k 0 :7936k 0 :7744k 0
:7744k 0
11M 0 : 11M 0 : 11M 0 : 11M 0 : 11M 0 : 11M 0 :
11M 0
19M 0 : 19M 0 : 19M 0 : 19M 0 : 19M 0 : 19M 0 :
19M 0
7488k 0 :7360k 0 :7296k 0 :7360k 0 :7296k 0 :7296k 0
:7296k 0
10M 0 : 10M 0 : 10M 0 : 10M 0 : 10M 0 : 10M 0 :
10M 0
14M 0 : 14M 0 : 14M 0 : 14M 0 : 14M 0 : 14M 0 :
14M 0
9472k 0 :9536k 0 :9536k 0 :9536k 0 :9472k 0 :9536k 0
:9472k 0
0 0 : 0 0 : 0 0 : 0 0 : 0 0 : 0 0 :
0 0
When I test the individual disks with
for disk in sdm sdl sdi sde sdk sdf sdd;do `dd if=/dev/$disk
of=/dev/null bs=1M count=1500 iflag=direct &` ;done
[root@san2 ~]# 1500+0 records in
1500+0 records out
1572864000 bytes (1.6 GB) copied, 8.96022 s, 176 MB/s
1500+0 records in
1500+0 records out
1572864000 bytes (1.6 GB) copied, 9.59289 s, 164 MB/s
1500+0 records in
1500+0 records out
1572864000 bytes (1.6 GB) copied, 10.0863 s, 156 MB/s
1500+0 records in
1500+0 records out
1572864000 bytes (1.6 GB) copied, 10.5833 s, 149 MB/s
1500+0 records in
1500+0 records out
1572864000 bytes (1.6 GB) copied, 10.6084 s, 148 MB/s
1500+0 records in
1500+0 records out
1572864000 bytes (1.6 GB) copied, 11.0205 s, 143 MB/s
1500+0 records in
1500+0 records out
1572864000 bytes (1.6 GB) copied, 11.3199 s, 139 MB/s
0 0 : 0 0 : 0 0 : 0 0 : 0 0 : 0 0 :
0 0
0 0 : 0 0 : 0 0 : 0 0 : 0 0 : 0 0 :
0 0
4096k 0 :5120k 0 : 32M 0 : 512k 0 : 29M 0 : 35M 0
:5120k 0
62M 0 : 51M 0 : 157M 0 : 145M 0 : 144M 0 : 153M 0 :
38M 0
153M 0 : 148M 0 : 158M 0 : 174M 0 : 135M 0 : 151M 0 :
150M 0
152M 0 : 144M 0 : 154M 0 : 179M 0 : 150M 0 : 146M 0 :
149M 0
149M 0 : 147M 0 : 155M 0 : 186M 0 : 148M 0 : 155M 0 :
157M 0
156M 0 : 128M 0 : 154M 0 : 188M 0 : 136M 0 : 153M 0 :
155M 0
159M 0 : 136M 0 : 157M 0 : 206M 0 : 147M 0 : 155M 0 :
151M 0
153M 0 : 147M 0 : 162M 0 : 153M 0 : 144M 0 : 127M 0 :
147M 0
153M 0 : 138M 0 : 159M 0 : 153M 0 : 134M 0 : 145M 0 :
146M 0
147M 0 : 144M 0 : 154M 0 : 116M 0 : 144M 0 : 153M 0 :
143M 0
154M 0 : 150M 0 : 60M 0 : 0 0 : 141M 0 : 131M 0 :
153M 0
61M 0 : 147M 0 : 0 0 : 0 0 : 51M 0 : 0 0 :
109M 0
0 0 : 17M 0 : 0 0 : 0 0 : 0 0 : 0 0 :
0 0
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