Hello,

I created a fresh VxVM 6.0 RAID5 volume on four columns. I performed
some basic I/O operations and noticed that writes always end in
read-modify-write cycle. I haven't been able to trigger a full stripe
writes yet, regardless of the command I used to write to the
filesystem. I tried with 64k and with 128k stripe width but in both
cases, I cannot get writes aligned. Filesystem is VxFS.
Below are outputs of my simple tests and configuration of the RAID5
volume. Any hints where I got it wrong?


1. dd example
root@mlincek:~# dd if=/dev/zero of=/mlincek/zero.dd bs=384k

root@mlincek:~# iostat -zxn 2
                    extended device statistics
    r/s    w/s   kr/s   kw/s wait actv wsvc_t asvc_t  %w  %b device
   69.0  115.4 8827.8 14777.0  0.0  0.4    0.0    2.3   0  41 c0t2d0
   69.0  115.4 8827.8 14777.0  0.0  0.3    0.0    1.4   0  25 c0t3d0
   70.0  115.4 8955.8 14777.0  0.0  0.4    0.0    2.0   0  36 c0t5d0
   69.5  115.9 8891.8 14841.0  0.0  0.4    0.0    2.2   0  41 c0t4d0

2. Copy file from another physical volume using cp command:

root@mlincek:~# cp testfile.tmp /mlincek/

                    extended device statistics
    r/s    w/s   kr/s   kw/s wait actv wsvc_t asvc_t  %w  %b device
   19.0  159.9 2250.5 20290.3  0.0  0.5    0.0    2.7   0  40 c0t2d0
   17.5  158.4 2239.0 20278.9  0.0  0.3    0.0    1.5   0  16 c0t3d0
   36.5  142.4 4489.5 18051.4  0.0  0.5    0.0    2.6   0  33 c0t5d0
   37.0  143.4 4494.0 18119.8  0.0  0.5    0.0    3.0   0  36 c0t4d0


3. Volume config

-bash-4.1# vxprint -g mlincekdg -t
...
dg mlincekdg    default      default  28000    1333350408.27.mlincek
dm mlincekdg01  disk_1       auto     65536    1953459328 -
dm mlincekdg02  disk_2       auto     65536    1953459328 -
dm mlincekdg03  disk_3       auto     65536    1953459328 -
dm mlincekdg04  disk_4       auto     65536    1953459328 -
sd mlincekdg01-01 mlincek-01 mlincekdg01 0     1953458944 0/0     disk_1   ENA
sd mlincekdg02-01 mlincek-01 mlincekdg02 0     1953458944 1/0     disk_2   ENA
sd mlincekdg03-01 mlincek-01 mlincekdg03 0     1953458944 2/0     disk_3   ENA
sd mlincekdg04-01 mlincek-01 mlincekdg04 0     1953458944 3/0     disk_4   ENA
pl mlincek-01   mlincek      ENABLED  ACTIVE   5860376832 RAID    4/256    RW
v  mlincek      -            ENABLED  ACTIVE   5860376832 RAID    -        raid5

-bash-4.1# /opt/VRTSvxfs/sbin/vxtunefs -p /mlincek
Filesystem i/o parameters for /mlincek
read_pref_io = 131072
read_nstream = 4
read_unit_io = 131072
write_pref_io = 393216
write_nstream = 1
write_unit_io = 131072
...


Mount: /mlincek on
/dev/vx/dsk/mlincekdg/mlincekread/write/setuid/devices/rstchown/delaylog/largefiles/ioerror=mwdisable/xattr/dev=3606d60

Volume was created with the following command:
root@mlincek:~# vxassist -g mlincekdg -o ordered make mlincek
5860376576 layout=raid5 nlog=0 ncol=4 stripewidth=128k mlincekdg01
mlincekdg02 mlincekdg03 mlincekdg04
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