For some reason, I am suffering very poor disk performance on RAID 10, but normal performance on RAID 5.
For context, I have 4 x 1 TB hard drives in a server. They are the physical volumes within the volume group.
PV VG Fmt Attr PSize PFree
/dev/sda1 vg lvm2 a-- <931.51g 0
/dev/sdb1 vg lvm2 a-- <931.51g 0
/dev/sdc1 vg lvm2 a-- <931.51g 0
/dev/sdd1 vg lvm2 a-- <931.51g 0
I created one RAID 10 logical volume with size 30 GB for the OS (root), and another RAID 5 logical volume with the rest of the free space for storing user data. Both span the whole 4 disks.
lvcreate --type raid10 --mirrors 1 --stripes 2 -L 30G -n root vglvcreate --type raid5 --stripes 3 -l 100%FREE -n data vg
When installing Debian on the root LV, the installer took more than two hours to complete. I knew something was wrong, so after the installation was complete, I ran a simple dd disk benchmark on the root LV, and got less than 10 Mb/s for the write performance. I then ran the same benchmark on the data LV, and got around 150 Mb/s.
As observed, the RAID 5 data LV is much faster, even though the RAID 10 root LV should outperform it in this case.
To confirm these benchmarks, I repeated the exact same install but on the data LV this time, and the installation took only 15 minutes.
Why is there such poor disk performance when using RAID 10? I have provided information about the CPU I'm using, if that's any help.
# dmidecode 3.3
Getting SMBIOS data from sysfs.
SMBIOS 2.5 present.
Handle 0x0004, DMI type 4, 40 bytes
Processor Information
Socket Designation: CPU 1
Type: Central Processor
Family: Unknown
Manufacturer: Intel
ID: 7A 06 01 00 FF FB EB BF
Version: Pentium(R) Dual-Core CPU E5200 @ 2.50GHz
Voltage: 1.2 V
External Clock: 200 MHz
Max Speed: 2500 MHz
Current Speed: 2500 MHz
Status: Populated, Enabled
Upgrade: Socket LGA775
L1 Cache Handle: 0x0005
L2 Cache Handle: 0x0006
L3 Cache Handle: 0x0007
Serial Number: To Be Filled By O.E.M.
Asset Tag: To Be Filled By O.E.M.
Part Number: To Be Filled By O.E.M.
Core Count: 2
Core Enabled: 2
Thread Count: 2
Characteristics:
64-bit capable
