Re: iostat - multiblock read count

hopehope_123 apparently said,on my timestamp of 26/05/2005 4:07 PM:

> by default for the ocfs. But since dd uses normal file io, this test
> fails. ( There exists a version of dd , cp commands for linux which
> uses direct io also.)

No worries, now I get it. There is a howto on the Linux Documentation Project website that goes in detail to all the tools available for accurate testing. Worth a search for these bits of doco: use "IO Performance" and have a quiet read. The problem with raw disk IO (and hence any IO that uses raw disks as base, including f/s) for 2.4 kernels is described in detail in one of them. Fixed on 2.4.17 onwards with the vary-io patch which is also referred in the Oracle doco mentioned before.

I'm toying around with test suites based on dd, 1M-32K-8K-4K-2K IO size for both cooked(file system) and raw IO, similar to yours. Some very surprising results in my systems, with net-based raid as well as native disks, raw and ext3! Once I finish making sense of the results will pop the scripts here or on dizwell for others to try.

> the point here is just to see whether the symptom tou mentiones exists
> on my stsem . ( 32kb. io barrier)

Really hard to click into unless raw: the file system layer masks it all out for me. In fact, after 8k it makes bugger all difference what the IO size is if using ext3.

-- 
Cheers
Nuno Souto
in sunny Sydney, Australia
wizofoz2k_at_yahoo.com.au.nospam