Re: Performance Characteristics of All Linux RAIDs (mdadm/bonnie++)

[Chris Snook <csnook@redhat.com>]

Justin Piszcz wrote:
> Hardware:
> 
> 1. Utilized (6) 400 gigabyte sata hard drives.
> 2. Everything is on PCI-e (965 chipset & a 2port sata card)
> 
> Used the following 'optimizations' for all tests.
> 
> # Set read-ahead.
> echo "Setting read-ahead to 64 MiB for /dev/md3"
> blockdev --setra 65536 /dev/md3
> 
> # Set stripe-cache_size for RAID5.
> echo "Setting stripe_cache_size to 16 MiB for /dev/md3"
> echo 16384 > /sys/block/md3/md/stripe_cache_size
> 
> # Disable NCQ on all disks.
> echo "Disabling NCQ on all disks..."
> for i in $DISKS
> do
>   echo "Disabling NCQ on $i"
>   echo 1 > /sys/block/"$i"/device/queue_depth
> done

Given that one of the greatest benefits of NCQ/TCQ is with parity RAID, 
I'd be fascinated to see how enabling NCQ changes your results.  Of 
course, you'd want to use a single SATA controller with a known good NCQ 
implementation, and hard drives known to not do stupid things like 
disable readahead when NCQ is enabled.

-- Chris