We are observing a strange performance drop on resync after an I/O is performed to a RAID5 device. This is using the RAID5 / md support in Linux 2.4.20. It is observable on at least two different disk controllers, so it doesn't appear to be a specific hardware limitation. To reproduce: (1) Create a RAID5 device, say /dev/md5, from four partitions on different disks, chunk-size = 256. (2) Observe resync performance vi 'cat /proc/mdstat'. We are seeing around 30MB/Sec on one controller, and 50+MB/sec on another. (3) Do a small read from the RAID device, such as 'dd if=/dev/md5 of=/dev/null bs=1024 count=1'. (4) Re-observe resync performance vi 'cat /proc/mdstat'. After the I/O, we are seeing resync drop by about 60%, to 11-12MB/Sec on one controller, and 15MB/sec on the other. The performance never recovers to the previous higher level, short of a reboot (which starts resync from the beginning) or recontructing the device. I/O to the individual sub-partitions does not impact this. We do not observe similar issues with RAID1. I ahve scoured the various lists and postings to find anything about this, but I haven't located anything. Thanks very much for any help that can be offered. Joel Lilienkamp - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
