Re: Performance Characteristics of All Linux RAIDs(mdadm/bonnie++)
From: Justin Piszcz
Date: Wed May 28 2008 - 13:54:18 EST
On Wed, 28 May 2008, Justin Piszcz wrote:
On Wed, 28 May 2008, Chris Snook wrote:
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.
Only/usually on multi-threaded jobs/tasks, yes?
Also, I turn off NCQ on all of my hosts that has it enabled by default
because
there are many bugs that occur when NCQ is on, they are working on it in the
libata layer but IMO it is not safe at all for running SATA disks w/NCQ as
with it on I have seen drives drop out of the array (with it off, no
problems).
I have done NCQ measurements in the past, for single threaded apps NCQ off
is the way to go, check this out from earlier (10 raptors raid5):
http://home.comcast.net/~jpiszcz/ncq_vs_noncq/
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