Can dbench be used for benchmarking fs?
Hello.
I use dbench for benchmarking the file systems and some results are suspicious for me.
I run 10 times dbench on ext3 and i have the following :
Throughput 16.6754 MB/sec (NB=20.8443 MB/sec 166.754 MBit/sec) Throughput 22.9772 MB/sec (NB=28.7216 MB/sec 229.772 MBit/sec) Throughput 22.3698 MB/sec (NB=27.9623 MB/sec 223.698 MBit/sec) Throughput 19.0533 MB/sec (NB=23.8167 MB/sec 190.533 MBit/sec) Throughput 21.9662 MB/sec (NB=27.4577 MB/sec 219.662 MBit/sec) Throughput 23.4062 MB/sec (NB=29.2578 MB/sec 234.062 MBit/sec) Throughput 21.4233 MB/sec (NB=26.7791 MB/sec 214.233 MBit/sec) Throughput 20.6202 MB/sec (NB=25.7753 MB/sec 206.202 MBit/sec) Throughput 15.7005 MB/sec (NB=19.6256 MB/sec 157.005 MBit/sec) Throughput 19.9631 MB/sec (NB=24.9538 MB/sec 199.631 MBit/sec)
As you can see
the average Throughput value is equal 20.4155 MB/sec the max value 23.4062 MB/sec and the min value 15.7005 MB/sec
As the result: the measuring deviation is equal = 23.4062 - 15.7005 = 7.7057 or about ~38% from average value.
I have dbench-1.1.tar.gz
I run dbench by the following way :
mke2fs -j /dev/xxx
mount /dev/xxx /mnt
cp dbench /mnt/.
cp clients.txt /mnt/.
cd /mnt
for x 1, 2, ... 10
do
./dbench 8 >>results
done
So, I have 2 questions :
1. Is there a way to avoid such big deviations on measuring a file systems throughput and to get more stable results?
2. Can dbench be used for benchmarking the file systems and if it is so -- what is the predictable error on the measuring?
Thank you very much for helping.
Lena.
Quoted 8 lines · E. Gryaznova
I use dbench for benchmarking the file systems and some results are suspicious for me.
:
:
:
As the result: the measuring deviation is equal = 23.4062 - 15.7005 = 7.7057 or about ~38% from average value.
Quoted 5 lines
So, I have 2 questions :
1. Is there a way to avoid such big deviations on measuring a file systems throughput and to get more stable results?
2. Can dbench be used for benchmarking the file systems and if it is so -- what is the predictable error on the measuring?
Dbench is not a good filesystem benchmark, because it deletes all of the files at the end. Use something else for the filesystem benchmark - there are lots of them (bonnie, iozone, mongo, etc).
Cheers, Andreas
--
Andreas Dilger
http://sourceforge.net/projects/ext2resize/
http://www-mddsp.enel.ucalgary.ca/People/adilger/
Quoted 9 lines · Andreas Dilger
Quoted 8 lines · E. Gryaznova
I use dbench for benchmarking the file systems and some results are suspicious for me.
:
:
:
As the result: the measuring deviation is equal = 23.4062 - 15.7005 = 7.7057 or about ~38% from average value.
Quoted 8 lines
Quoted 5 lines
So, I have 2 questions :
1. Is there a way to avoid such big deviations on measuring a file systems throughput and to get more stable results?
2. Can dbench be used for benchmarking the file systems and if it is so -- what is the predictable error on the measuring?Dbench is not a good filesystem benchmark, because it deletes all of the files at the end. Use something else for the filesystem benchmark - there
Err... What is wrong with deleting all files at the end? Or do you mean it should mix file operations during run?
Quoted 1 line
are lots of them (bonnie, iozone, mongo, etc).
But why variance is so large?
Another probably interesting observation is that dbench works faster on ext2 if it is run directly after mkfs.ext2, that is, without reboot between mkfs and mount.
Quoted 2 lines
Cheers, Andreas
Nikita.
Quoted 19 lines · Nikita Danilov
Quoted 9 lines · Andreas Dilger
Quoted 8 lines · E. Gryaznova
I use dbench for benchmarking the file systems and some results are suspicious for me.
:
:
:
As the result: the measuring deviation is equal = 23.4062 - 15.7005 = 7.7057 or about ~38% from average value.Quoted 8 lines
Quoted 5 lines
So, I have 2 questions :
1. Is there a way to avoid such big deviations on measuring a file systems throughput and to get more stable results?
2. Can dbench be used for benchmarking the file systems and if it is so -- what is the predictable error on the measuring?Dbench is not a good filesystem benchmark, because it deletes all of the files at the end. Use something else for the filesystem benchmark - there
Quoted 6 lines
Err... What is wrong with deleting all files at the end? Or do you mean it should mix file operations during run?
Quoted 1 line
are lots of them (bonnie, iozone, mongo, etc).
But why variance is so large?
Dbench is a bad filesystem benchmark because if all (or some large part) of the files are deleted before the VM flushes them to disk, then you are not really testing filesystem performance very much. If you have enough RAM in your system and a fast enough CPU you could complete the entire dbench run without ever writing any data to disk. There is some filesystem activity (you need to create files and map pages), but it isn't a good test of filesystem throughput.
The reason there is so much variability in the tests is that if the test takes even a small amount more time to run this means more data gets flushed to disk by the VM (instead of being deleted and never written), making the test run longer and even _more_ data needs to get written, etc.
Dbench is a good multi-threaded filesystem stress program, but it isn't a good benchmark.
Cheers, Andreas
--
Andreas Dilger
http://sourceforge.net/projects/ext2resize/
http://www-mddsp.enel.ucalgary.ca/People/adilger/