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

[Bill Davidsen <davidsen@xxxxxxx>]

Justin Piszcz wrote:
> On Thu, 29 May 2008, Holger Kiehl wrote:
>
> > On Wed, 28 May 2008, 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
> > >
> > > Software:
> > >
> > > Kernel: 2.6.23.1 x86_64
> > > Filesystem: XFS
> > > Mount options: defaults,noatime
> > >
> > > Results:
> > >
> > > http://home.comcast.net/~jpiszcz/raid/20080528/raid-levels.html
> > > http://home.comcast.net/~jpiszcz/raid/20080528/raid-levels.txt
> > Why is the Sequential Output (Block) for raid6 165719 and for raid5 only
> > 86797? I would have thought that raid6 was always a bit slower in 
> > writting
> > due to having to write double amount of parity data.
> >
> > Holger
>
> RAID5 (2nd test of 3 averaged runs) & Single disk added:
> http://home.comcast.net/~jpiszcz/raid/20080528/raid-levels.html 

Other than repeating my (possibly lost) comment that this would be 
vastly easier to read if the number were aligned and all had the same 
number of decimal places in a single column, good stuff. For sequential 
i/o the winners and losers are clear, and you can set cost and 
performance to pick the winners. Seems obvious that raid-1 is the loser 
for single threaded load, I suspect that it would be poor against other 
levels in multithread loads, but not so much for read.

--
Bill Davidsen <davidsen@xxxxxxx>
 "Woe unto the statesman who makes war without a reason that will still
 be valid when the war is over..." Otto von Bismark 


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