--- Robert Watson <[EMAIL PROTECTED]> wrote:
On Sat, 30 Apr 2005, Arne WXrner wrote:
3. The man page geom(4) of R5.3 says "The GEOM framework provides an infrastructure in which "classes" can per- form transformations on disk I/O requests on their path from the upper kernel to the device drivers and back.
Could it be, that geom slows something down (in some boxes the
reading ops are very slow; in my box the writing ops are very slow)?
[...] against a further offset region of ad0. If they're against the same bits of disk, the main difference here will be the additional processing of the layers in the stack. A little bit of math is required to figure out the offset, but dd should be usable to figure out the incremental cost.
I used the following commands: 1. dd if=/dev/ad0s2a bs=16k count=10000 of=/dev/null 2. dd if=/dev/ad0 iseek=2100357 bs=16k count=10000 of=/dev/null (I think I did the math correctly; indeed the read speed of my ad0 varies between 45MB/sec (iseek=0) and 25MB/sec (in the end) with bs=128k). The results were nearly the same (both between 26MB/sec and 28MB/sec). Maybe I should have done it in single user mode.
My other hard disc ad1 (it is newer and bigger and faster and more furious) behaves better (but I can just try writing via the file system (ufs+s) and a final sync): The sync just needs .24sec of 18.28 seconds; the read and write speed is nearly the same (about 37MB/sec+/-1MB/sec).
Is there anything else, that could help to find the reason for the difference between ad0's speed in R4.11 and R5.3?
I'll be honest here, I don't care much if the speed difference between 4.X and 5.X is measureable, or whatever. What I find is a little telling of an issue somewhere, is that READS are slower than WRITES! This is totally bogus to me - dd'ing a file to a filesystem, then umounting should take longer than dd'ing from the disk to /dev/null, it nearly every config I can dream up. Maybe it's the speed at which /dev/null can gobble bits (seems highly unlikely!), or maybe GEOM is busy doing a check or some routine to data being accessed directly from the disk device instead of through a filesystem? I don't know, but it is an issue, and I'm sure we'll get nailed up to a fence in some benchmark somewhere if we don't fix it..
Eric
-- ------------------------------------------------------------------------ Eric Anderson Sr. Systems Administrator Centaur Technology A lost ounce of gold may be found, a lost moment of time never. ------------------------------------------------------------------------
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