Re: [Scst-devel] Integration of SCST in the mainstream Linux kernel

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Vladislav Bolkhovitin wrote:
Bart Van Assche wrote:

[...]

I can run disktest on the same setups I ran dd on. This will take some
time however.

Disktest was already referenced in the beginning of the performance comparison thread, but its results are not very interesting if we are going to find out, which implementation is more effective, because in the modes, in which usually people run this utility, it produces latency insensitive workload (multiple threads working in parallel). So, such

There are other issues with disktest, in that you can easily specify option combinations that generate apparently 5+ GB/s of IO, though actual traffic over the link to storage is very low. Caveat disktest emptor.

multithreaded disktests results will be different between STGT and SCST only if STGT's implementation will get target CPU bound. If CPU on the target is powerful enough, even extra busy loops in the STGT or SCST hot path code will change nothing.

Additionally, multithreaded disktest over RAM disk is a good example of a synthetic benchmark, which has almost no relation with real life workloads. But people like it, because it produces nice looking results.

I agree. The backing store should be a disk for it to have meaning, though please note my caveat above.


Actually, I don't know what kind of conclusions it is possible to make from disktest's results (maybe only how throughput gets bigger or slower with increasing number of threads?), it's a good stress test tool, but not more.

Unfortunately, I agree. Bonnie++, dd tests, and a few others seem to bear far closer to "real world" tests than disktest and iozone, the latter of which does more to test the speed of RAM cache and system call performance than actual IO.


Disktest is new to me -- any hints with regard to suitable
combinations of command line parameters are welcome. The most recent
version I could find on http://ltp.sourceforge.net/ is ltp-20071231.

Bart Van Assche.

Here is what I have run:

disktest -K 8 -B 256k  -I F -N 20000000 -P A -w /big/file
disktest -K 8 -B 64k   -I F -N 20000000 -P A -w /big/file
disktest -K 8 -B 1k    -I B -N 2000000  -P A  /dev/sdb2

and many others.



Joe


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