I'm have RAID 5 on Synology DS1813+ (DSM Version: DSM 5.0-4493 Update 4) with 8 ST4000DM000-1F2168 disk, usind as NAS and iSCSI/NFS targer for ESXi.
In low read/write rate from disk have more io wait, please have you any ideas?
SRV1> uname -a
Linux SRV1 3.2.40 #4493 SMP Thu Aug 21 21:46:06 CST 2014 x86_64 GNU/Linux synology_cedarview_1813+
nmon output
DiskName Busy Read WriteKB
sda 63% 0.0 0.0
sda1 0% 0.0 0.0
sda2 28% 115.7 0.0
sda3 50% 0.0 0.0
sdb 50% 0.0 0.0
sdb1 0% 0.0 0.0
sdb2 20% 85.8 0.0
sdb3 37% 0.0 0.0
<skip omitted>
Totals Read-MB/s=0.7 Writes-MB/s=0.0 Transfers/sec=884.8
CPU output
CPU User% Sys% Wait% Idle
1 0.5 2.5 76.9 20.1
2 0.0 1.0 59.1 39.9
3 0.0 19.1 18.1 62.8
4 0.0 2.5 18.5 79.0
RAID info:
SRV1> mdadm --detail /dev/md2
/dev/md2:
Version : 1.2
Creation Time : Mon Jan 20 12:26:15 2014
Raid Level : raid5
Array Size : 27316073792 (26050.64 GiB 27971.66 GB)
Used Dev Size : 3902296256 (3721.52 GiB 3995.95 GB)
Raid Devices : 8
Total Devices : 8
Persistence : Superblock is persistent
Update Time : Mon Jan 18 08:51:10 2016
State : clean
Active Devices : 8
Working Devices : 8
Failed Devices : 0
Spare Devices : 0
Layout : left-symmetric
Chunk Size : 64K
Name : SRV1:2 (local to host SRV1)
UUID : 690db49f:cc6aebea:e4dc7a24:b8c4a142
Events : 66
Number Major Minor RaidDevice State
0 8 3 0 active sync /dev/hda3
1 8 19 1 active sync /dev/hdb3
2 8 35 2 active sync /dev/hdc3
3 8 51 3 active sync /dev/sdd3
4 8 67 4 active sync /dev/hde3
5 8 83 5 active sync /dev/sdf3
6 8 99 6 active sync /dev/sdg3
7 8 115 7 active sync /dev/sdh3
In dmesg:
[23334402.188177] __fd_async_epio_request_handle: 6 callbacks suppressed
[23334402.194671] iSCSI: iSCSI: EPIO[/volume1/@iSCSITrg/iSCSI_3_Extent_LUN-L1_000], opcode[89], error(-65539), pos(10578606080)
[23334402.194937] iSCSI: iSCSI: EPIO[/volume1/@iSCSITrg/iSCSI_3_Extent_LUN-L1_000], opcode[89], error(-65539), pos(10578606080)