amird driver, BDFLUSH and NAUTOUP, and more

Fri Aug 13 19:44:29 2004 amird driver, BDFLUSH and NAUTOUP, and more
Posted by Tony Lawrence
Search Keys: performance,kernel,disks,raid

I recently installed a new SCO 5.0.7 server to replace an older SCO 5.0.5 system. We put in new hardware, with an LSI Ultra-320 raid controller. Two drives were configured for hardware mirroring. That hardware uses the AMIRD driver, and the installation was quick and simple.

I checked disk performance against the old server with various permutations of "timex dd if=/dev/root of=/tmp/this bs=1024 count=8192", using different block sizes and counts, and also adding some seeks. I did these on both machines, with some tests including intermediate "ls -lR /u" to clear the buffer cache and some not, and in general I could say that the new machine was 6 times faster for disk access and a little more so for buffer cache accesses.

Imagine my surprise when the customer reported that it seemed slower to them.

Well, I knew that /etc/idrc.d/amird might be at fault, so I added an "exit 0" at the top of that script and killed the /etc/amirdmon process that it had started. That helped a little, but they still complained of sluggishness. I could see that in "sar -d", too:

12:00:00 Sdsk-0    26.95      1.00      0.67      5.30      0.00    400.15

12:20:00 Sdsk-0     9.58      1.00      0.82      2.92      0.00    116.44

12:40:01 Sdsk-0     9.65      1.00      0.72      1.92      0.00    134.11

13:00:03 Sdsk-0     5.81      1.00      1.17      5.15      0.00     49.57

13:20:00 Sdsk-0     6.28      1.00      0.42      1.07      0.00    148.58

13:40:00 Sdsk-0     2.10      1.00      0.12      0.27      0.00    179.93

14:00:00 Sdsk-0    24.20      1.01      1.72      6.52      1.44    141.05

14:20:00 Sdsk-0    29.65      1.01      0.57      1.42      5.85    517.83

14:40:00 Sdsk-0    29.33      1.00      2.12      6.13      0.00    138.62

15:00:00 Sdsk-0    15.44      1.00      1.16      2.98      0.00    133.49

15:20:00 Sdsk-0   100.00      1.01      5.61     19.16      2.28    322.97


Average  Sdsk-0    48.04      1.02      1.43      6.29      6.55    336.06
 

I couldn't get the command line scodb to work for me over my ssh connection, so I had to use /etc/conf/cf.d/configure to modify BDFLUSH and NAUTOUP to "1". . Relink, reboot, and sar was much happier:

15:38:41  device   %busy     avque     r+w/s    blks/s    avwait    avserv (-d)
15:38:56 Sdsk-0     0.20      1.00      1.93      4.40      0.00      1.03

15:39:11 Sdsk-0     0.07      1.00      2.13      7.73      0.00      0.31

15:39:26 Sdsk-0     1.53      1.00      3.40     10.93      0.00      4.51

15:39:41 Sdsk-0     1.33      1.00      3.40     11.59      0.00      3.92

15:39:56 Sdsk-0     1.00      1.00      1.33      2.93      0.00      7.50

15:40:11 Sdsk-0     1.60      1.00      4.27     13.87      0.00      3.75

15:40:26 Sdsk-0     0.07      1.00      0.27      0.67      0.00      2.50

15:40:41 Sdsk-0     1.60      1.00      4.13     10.80      0.00      3.87

15:40:56 Sdsk-0     0.13      1.00      1.27      4.40      0.00      1.05

15:41:11 Sdsk-0     0.40      1.00      1.67      6.93      0.00      2.40
 

The users were now able to agree that the system was faster.

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