Hi, > Dstat could at least tell you if your problem is CPU or I/O. This was the result of running the following command which I obtained from reading up about two weeks ago when I started trying to investigate the abnormal server behaviour. dstat -c --top-cpu -d --top-bio --top-latency usr sys idl wai hiq siq| cpu process | read writ| latency process 4 1 93 2 0 0|mysqld 0.0| 80k 82k|khelper 8 42 46 0 12 0 0|httpd 12| 648k 0 |ksoftirqd/0 111 26 37 12 26 0 0|httpd 1.5| 520k 11M|ksoftirqd/1 75 23 49 8 19 0 0|exim 1.0| 652k 16k|ksoftirqd/0 44 26 44 3 28 0 0|exim 1.0| 652k 1296k|ksoftirqd/0 44 32 41 4 23 0 0|exim 1.5| 620k 16k|ksoftirqd/0 50 28 52 3 16 0 0|exim 1.5| 700k 0 |ksoftirqd/1 47 21 41 11 28 0 0|exim 1.0| 556k 11M|ksoftirqd/0 79 27 46 3 24 0 0|exim 1.5| 684k 16k|ksoftirqd/1 40 29 45 2 24 0 0|exim 1.0| 672k 944k|ksoftirqd/0 25 28 33 3 37 0 0|httpd 14| 852k 5992k|ksoftirqd/1 39 36 39 2 23 0 0|httpd 5.0|1024k 0 |ksoftirqd/0 84 > Even better, run > > vmstat 2 10 > > Look at the first two columns. What column have higher numbers? If r, > you're CPU-bound. If b, you're I/O bound. procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu------ r b swpd free buff cache si so bi bo in cs us sy id wa st 8 1 3092 131460 100692 833668 0 0 40 21 1 0 4 1 92 2 0 9 1 3092 130708 100700 835016 0 0 578 206 577 1420 32 50 3 15 0 7 1 3092 128324 100716 836148 0 0 546 2866 594 1465 31 44 7 18 0 4 1 3092 126860 100724 837268 0 0 540 256 596 1505 28 43 6 23 0 7 2 3092 125600 100740 838564 0 0 620 234 661 1442 30 41 2 26 0 5 1 3092 124028 100756 839752 0 0 570 2692 635 1430 24 45 6 25 0 6 0 3092 122040 100784 840964 0 0 584 1464 682 1434 27 44 2 28 0 6 1 3092 120588 100792 842232 0 0 602 278 624 1562 32 46 2 20 0 2 3 3092 120556 100840 843064 0 0 440 2908 603 1299 22 35 6 37 0 3 1 3092 119832 100876 844088 0 0 430 1104 605 1348 23 36 1 40 0 According to this, am I correct to conclude that I'm CPU bound and the system is busy doing some unknown processing? > Did you check if you have a defect disk or a rebuilding array? That > could be the cause. I usually run a "cat /proc/mdstat" whenever I log into the server to check my MD raid status. So far the array appears ok. There are no disk warning when I run "dmesg". smartctl also reports no error logged and passed for both disks, although no self test was ran. Would I be safe to conclude that the disks are OK and not part of the problem? Thanks again to everybody for the suggestions and help so far.