On Wed, Dec 31, 2008 at 17:35, Mike McGrath <mmcgr...@redhat.com> wrote:
> On Wed, 31 Dec 2008, Corey Chandler wrote: > > > Mike McGrath wrote: > > > Lets pool some knowledge together because at this point, I'm missing > > > something. > > > > > > I've been doing all measurements with sar as bonnie, etc, causes builds > to > > > timeout. > > > > > > Problem: We're seeing slower then normal disk IO. At least I think we > > > are. This is a PERC5/E and MD1000 array. > > > > > > > 1. Are we sure the array hasn't lost a drive? > > I can't physically look at the drive (they're a couple hundred miles away) > but we've seen no reports of it (via the drac anyway). I'll have to get > the raid software on there to be for sure. I'd think a degraded raid > array would affect both direct block access and file level access. > > > 2. What's your scheduler set to? CFQ tends to not work in many > applications > > where the deadline scheduler works better... > > > > I'd tried other schedulers earlier but they didn't seem to make much of a > difference. Even still, I'll get dealine setup and take a look. > > At least we've got the dd and cat problem figured out. Now to figure out > why there's such a discrepancy between file level reads and block level > reads. Anyone else have an array of this type and size to run those tests > on? I'd be curious to see what others are getting. > we are working on a rhel3 to 5 migration at my job. We have 2 primary filesystems. one is large database files and the other is lots of small documents. As we were testing backup software for rhel5 we noticed a 60% decrease in speed moving from rhel3 to rhel5 with the same file system, but only on the document filesystem, the db file system was perfectly snappy. After a lot of troubleshooting it was deemed to be related to the dir_index btree hash. The path was to long before there was a difference in the names of the files, making the index incredibly slow. Removing dir_index recovered a bit of the difference, but didn't resolve the issue. A quick rename of one of the base directories recovered almost the entire 60%. Thought I'd at least throw it out there, although I'm not sure that it is the exact issue, it doesn't hurt to have it floating in the background. -greg/xaeth
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