I've been dealing with an interesting situation here regarding a system that is running three software RAID arrays. The layout consists of two RAID1 arrays sharing two IDE drives and a RAID5 array running on five SCSI drives (four active and one on hot standby). Latency tests on the system show a very regular series of latency spikes occurring at around 5.2 second intervals during the disk write phase. They do not appear to be particularly related to the underlying physical bus -- they appear in tests of both the IDE and SCSI based arrays. Even more interestingly, disk tuning and/or application of the ll patch seem to make very little difference in the test results.
I've posted the test results at http://www.wava.com/ll_results. Has anyone out there done any work regarding RAID as it bears upon low latency? Cheers! |-------------------------------------------------------------------------| |Frederick F. Gleason, Jr.|WAVA Radio - 105 FM |Voice: 1-(703)-807-2266 | | Director of Engineering |1901 N. Moore Street| FAX: 1-(703)-807-2245 | | |Arlington, VA 22209 | Web: HTTP://www.wava.com| |-------------------------------------------------------------------------| | Documentation is like castor oil: managers know it must be good | | because programmers hate writing it so much. | | -- Anonymous | |-------------------------------------------------------------------------|
