On Tue, 21 Jan 2014 10:42:19 -0600 Jon Nelson
<jnelson-linux-raid@xxxxxxxxxxx> wrote:
> 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.
A 5 disk RAID6 has 3 data drives (in each stripe), so 250MB/s translates to
250/3 or 83MB/s per drive (skipping over parity data isn't faster than
reading it unless you have a very large chunk size, which brings other costs).
What exactly where you hoping for?
If you run something like
for i in a b c d e
do dd if=/dev/sd${i}3 of=/dev/null bs=1M count=100 &
done
while system is otherwise idle, what throughput does each dd report?
NeilBrown
>
> 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?
>
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