I have a 5-disk RAID6 using (5) 320GB SATA drives.
I rarely see even sequential I/O approaching that of a single drive's
performance.
Example: (Rarely!) I'll see an aggregate 250MB/s read or write, but
that translates to 50MB/s read or write per-drive. I was hoping for
more.
The partition layout looks like this:
/dev/sda1 : start= 2048, size= 1024000, Id=83, bootable
/dev/sda2 : start= 1026048, size= 1024000, Id=82
/dev/sda3 : start= 2050048, size=623091712, Id=fd
/dev/sda4 : start= 0, size= 0, Id= 0
on all 5 disks, and sd{whatever}3 is used to assemble the raid,
specifically, /dev/md2.
mdadm -D /dev/md2:
/dev/md2:
Version : 1.2
Creation Time : Fri Nov 1 11:13:07 2013
Raid Level : raid6
Array Size : 934242816 (890.96 GiB 956.66 GB)
Used Dev Size : 311414272 (296.99 GiB 318.89 GB)
Raid Devices : 5
Total Devices : 5
Persistence : Superblock is persistent
Intent Bitmap : Internal
Update Time : Tue Jan 21 10:33:52 2014
State : active
Active Devices : 5
Working Devices : 5
Failed Devices : 0
Spare Devices : 0
Layout : left-symmetric
Chunk Size : 64K
Name : turnip:2 (local to host turnip)
UUID : bece804d:eaaeb280:38d2d7f3:1e493146
Events : 21788
Number Major Minor RaidDevice State
0 8 51 0 active sync /dev/sdd3
1 8 35 1 active sync /dev/sdc3
2 8 3 2 active sync /dev/sda3
3 8 19 3 active sync /dev/sdb3
4 8 67 4 active sync /dev/sde3
The filesystem is ext4, and debugfs says:
RAID stride: 16
RAID stripe width: 48
The processor is an AMD Phenom 9150e (quad-core, x86_64) and the O/S
is openSUSE 13.1, kernel 3.11.6. Some of the hardware looks like this:
00:00.0 Host bridge: Advanced Micro Devices, Inc. [AMD] RS780 Host Bridge
00:01.0 PCI bridge: Advanced Micro Devices, Inc. [AMD] RS780/RS880 PCI
to PCI bridge (int gfx)
00:07.0 PCI bridge: Advanced Micro Devices, Inc. [AMD] RS780/RS880 PCI
to PCI bridge (PCIE port 3)
00:11.0 SATA controller: Advanced Micro Devices, Inc. [AMD/ATI]
SB7x0/SB8x0/SB9x0 SATA Controller [AHCI mode]
Settings:
The stripe_cache_size is 4096 (see
http://blog.jamponi.net/2013/12/sw-raid6-performance-influenced-by.html
)
readahead is 16384
scheduler is deadline
queue depth per-drive is 1.
nr_requests is 256.
Does this seem out of line? Thoughts?
--
Jon
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