RA8?, RL02 interleave factors (long)

[dan at msdc.UUCP]

I had my interest tweaked by all the questions on disk interleaving, so
I thought I'd apply some brute force to complement the subtle logic
applied by others.  The results were somewhat surprising, so I thought
y'all might be interested [note the appropriate use of the second person
plural pronoun :-)].  I also suspect that not many folks have
completely idle systems to fiddle with, either.

We are running 4.1bsd on 750s with RL02s, RA80s and RA81s in various
mixes.  I ran various combinations of interleave factors for the
various disks reading and writing a 2MB (2^20B) file.  I have no faith
in the "writing" numbers, since I was copying a file from another drive
with different interleave, so I've included summaries of only the
reading elapsed times (the user and system times were nearly identical
in all cases).  The systems were quiescent except for cron waking up to
do nothing and a uucp logging in every 5 minutes or so.  These might
skew a single trial, so I did the reads twice.

First, here's the script I used to make it happen:
------
for x in 3 5 7 9 11 13 15 17; do
    for y in 15 30 60 120 217 434; do
        echo "m n: $x $y"
        fsck -s$y:$x /dev/ra0f >/dev/null
        mount /dev/ra0f /b2
        echo -n "    Writing:    "
        time sh -c "dd if=/usr/tmp/bigfile of=/b2/test bs=10240 >/dev/null 2>&1"
        echo -n "    Reading:    "
        time sh -c "dd if=/b2/test of=/dev/null bs=10240 >/dev/null 2>&1"
        echo -n "    Reading:    "
        time sh -c "dd if=/b2/test of=/dev/null bs=10240 >/dev/null 2>&1"
        rm -f /b2/test
        umount /dev/ra0f
    done
done
------

And now, here are the numbers.  One column is for each device type,
with the interleave factors and average elapsed read time for a 2MB
file (using 'dd' with bs=10240).  They are presented in order of
increasing average time.

------RL02------      ------RA80------      ------RA81------
  m   n   Times         m   n   Times         m   n   Times
  3   10  23 24         7   30  18 18        11  208  23 22
  4   10  25 26         7  217  18 18        11  728  23 22
  3   20  26 26         7  434  18 18        11  364  23 23
  3   40  29 28         7   15  18 19        10  728  24 23
  2   10  29 29         7  120  19 18        11   52  24 24
  2    5  31 29         5   30  22 21        11  104  24 24
  3    5  31 31         7   60  21 22        12  728  24 25
  5   10  31 31         5   60  22 22        11   26  25 25
  2   20  31 32         5   15  20 25        13  728  25 25
  2   40  33 32         5  120  22 23        12   26  26 26
  4   20  33 33         5  217  22 23        13  208  26 26
  4   40  34 34         9  434  23 22        13  364  26 26
  6   10  36 35         5  434  23 23        13  104  27 26
  5   20  41 40         9   15  23 23        10   26  27 28
  4    5  42 41         9   30  24 23        13   26  28 27
  5   40  42 41         9  120  24 23        15  728  28 28
  6   40  48 48         9   60  24 24        13   52  29 28
  6   20  49 48         9  217  27 23        15  104  29 29
                        3   60  26 25        15  208  30 28
                        3  120  26 25        15  364  29 29
                        3  434  25 26        15   26  29 30
                        3   30  26 26         9   52  30 30
                        3  217  26 26         9   26  31 31
                        3   15  27 26         9  104  31 31
                       11  120  27 27         9  208  31 31
                       11   30  27 28         9  364  31 31
                       11  217  27 28         9  728  31 32
                       11   15  27 29        15   52  31 32
                       11   60  28 28        17   26  32 31
                       11  434  32 27        17  728  32 31
                       17   60  31 30        17  364  32 32
                       13   15  32 31        17  208  33 32
                       13   60  32 31        17  104  34 33
                       13  434  32 31         7   52  39 37
                       15  120  32 32         7  364  39 38
                       13   30  33 32         7   26  39 39
                       13  120  32 34         7  208  39 39
                       13  217  33 33         7  728  39 39
                       15  217  33 33         5   26  40 39
                       15  434  33 33         5  104  40 39
                       15   60  33 34         5  208  39 40
                       17   15  34 33         5  728  39 40
                       17  120  35 35         7  104  40 39
                       15   30  36 36        17   52  36 43
                       17   30  37 36         3   26  40 40
                       17  217  37 36         5   52  40 40
                       15   15  37 38         5  364  40 40
                       17  434  38 37         3  104  41 40
                                              3  208  41 40
                                              3  364  41 41
                                              3  728  41 41
                                              3   52  42 41

I welcome comments on the interpretation of these numbers.  I'd
especially like to know why the RA81s are so much slower than the
RA80s.

Dan Forsyth (allegra!akgua!msdc!dan, decvax!duke!mcnc!msdc!dan)
Medical Systems Development Corp, Atlanta