Hello,
I have a raid5 array consisting of 4 8TB disks connected via USB3.
[ml@xenia ~]$ cat /proc/mdstat
Personalities : [raid6] [raid5] [raid4]
md127 : active raid5 sde1[4] sdc1[1] sdd1[2] sdb1[0]
23441682432 blocks super 1.2 level 5, 512k chunk, algorithm 2
[4/4] [UUUU]
bitmap: 0/59 pages [0KB], 65536KB chunk
unused devices: <none>
[ml@xenia ~]$
Up to and including kernel 4.20.13-arch1 everything is fine and I get
reasonable performance:
[root@xenia ml]# dd if=/dev/md127 of=/dev/null bs=2M status=progress
3078619136 bytes (3,1 GB, 2,9 GiB) copied, 13 s, 237 MB/s^C
1516+0 Datensätze ein
1515+0 Datensätze aus
3177185280 bytes (3,2 GB, 3,0 GiB) copied, 13,4403 s, 236 MB/s
[root@xenia ml]# uname -a
Linux xenia.leun.net 4.20.13-arch1-1-ARCH #1 SMP PREEMPT Wed Feb 27
19:10:28 UTC 2019 x86_64 GNU/Linux
[root@xenia ml]#
With kernel 5.0.0-arch1-1-ARCH (also verified that with kernel.org
5.0.0) I get PAINFULLY slow performance on the raid, but the performance
of the disks the array consists of is ok:
[root@xenia ml]# dd if=/dev/md127 of=/dev/null bs=2M status=progress
6291456 bytes (6,3 MB, 6,0 MiB) copied, 41 s, 154 kB/s^C
4+0 Datensätze ein
3+0 Datensätze aus
6291456 bytes (6,3 MB, 6,0 MiB) copied, 59,0605 s, 107 kB/s
[root@xenia ml]# dd if=/dev/sdb1 of=/dev/null bs=2M status=progress
1642070016 bytes (1,6 GB, 1,5 GiB) copied, 8 s, 205 MB/s^C
806+0 Datensätze ein
805+0 Datensätze aus
1688207360 bytes (1,7 GB, 1,6 GiB) copied, 8,23402 s, 205 MB/s
[root@xenia ml]#
(The other 3 disks show the same speed)
Any idea why it is THAT slow?
Best Regards,
Michael Leun
