Messages in this thread | | | Date | Thu, 28 Feb 2008 15:30:03 -0500 | From | Bill Davidsen <> | Subject | Re: Linux and SSD and how to decrease io delay : question, please |
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Mariella Petrini wrote: > Hi All, > > I have been running Linux kernel 2.6.23 with Debian on > > a 2 CPUs Dual-Core AMD Opteron(tm) Processor 2218. > I have been using an SSD drive (MTRON) connected to a > raid controller (LSI MegaRAID 8704ELP) to contain > data stored on several databases. > Each database contains 20,000 files and there are 50 > databases total (1,000,000 files distributed across 50 > directories on the filesystem on the ssd). > > The database server uses the databases very "write" > intensively. > An approximate percentage could be 20% reads versus > 80% random writes. > > No matter which filesystem type is used (I have tried > ext3, xfs, jfs, reiserfs) I see every few seconds > snapshots (the could last in the worst case up to 200 > seconds, depending on the filesystem type) > where the iowait on the ssd device goes approximately > over 50% (up to 100%) and > the database server threads go to wait (get > suspended). > > Is there any Linux kernel parameter or any Linux > parameter that could be varied that could help to > decrease the time spent to sync all the data to the > SSD device ? > I may misunderstand the problem, but have you tried tuning the parameters /proc/sys/vm/dirty_* to help this? It sounds as if you may be filling write cache and then flushing. Of course you didn't measure the disk i/o rates along with this, so it's hard to see what's happening.
-- Bill Davidsen <davidsen@tmr.com> "We have more to fear from the bungling of the incompetent than from the machinations of the wicked." - from Slashdot
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