>>> On Tue, 17 Jan 2012 01:09:34 +0100, Wim Delvaux >>> <wrl.delvaux@xxxxxxxxx> said: > Hi all, I have two 2TB disks half set up using raid 1 (full > mirroring ?) and the other half using striping. very > frequently my system, a kubuntu 11.10, hangs (gui is > unresponsive). pressing alt-esc to popup the process monitor > shows that key processes are hanging on disk-sleep. Often this > is the flush daemon or the mdadm processes or sometimes just > two or three applications. It could be many different reasons. You should check 'dmesg' and run run 'vmstat 1' in a window while this happens. Most likely causes: - Your 2TB disks have long fixed error recovery timeouts and some sectors are going bad. In this case there is no fix other than replacing the disks. - The disks literally go to 'sleep' (that is power-saving mode). The fix here is to specify 'hdparm -S 0'. - The disk elevator keeps starving reads or writes during high disk activity. The fix here is to use 'deadline' which is known to have fewer starvation bugs than others. - A lot of unwritten pages are allowed to accumulate in memory, and the flush daemon and other applications hang while they are being written out. The fix here is to specify a small value for 'dirty_background_ratio' (like 1 or 2) and a large one for 'dirty_ratio' (like 40 or 50), or equivalent '_bytes'. - Since you have 8GiB of RAM, this is least likely: high traffic on the swap space combined with the very bad page swap logic in the Linux kernel. Usually it is large values of 'dirty_background_ratio' on large-memory configurations. [ ... ] -- 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