Dear,

I set up zfs volume, and export via nfs on freebsd8.1.
It mounts by client, and vdbench is executed. 
The kernel panic is occurred.

The detailed procedure is as follows. 

--- nfs server(freebsd8.1 amd64) ---
<</dev/mfid0s2>>
The data for partition 2 is:
sysid 165 (0xa5),(FreeBSD/NetBSD/386BSD)
    start 40949685, size 244718145 (119491 Meg), flag 0
	beg: cyl 501/ head 0/ sector 1;
	end: cyl 373/ head 254/ sector 63
<</dev/mfid1s2>>
The data for partition 2 is:
sysid 165 (0xa5),(FreeBSD/NetBSD/386BSD)
    start 40949685, size 244718145 (119491 Meg), flag 0
	beg: cyl 501/ head 0/ sector 1;
	end: cyl 373/ head 254/ sector 63
<</dev/mfid2s2>>
The data for partition 2 is:
sysid 165 (0xa5),(FreeBSD/NetBSD/386BSD)
    start 40949685, size 244718145 (119491 Meg), flag 0
	beg: cyl 501/ head 0/ sector 1;
	end: cyl 373/ head 254/ sector 63

# zpool create expdsk raidz mfid0s2 mfid1s2 mfid2s2
# zpool status
     pool: expdsk
     state: ONLINE
     scrub: none requested
     config:

       NAME         STATE     READ WRITE CKSUM
       expdsk       ONLINE       0     0     0
         raidz1     ONLINE       0     0     0
           mfid0s2  ONLINE       0     0     0
           mfid1s2  ONLINE       0     0     0
           mfid2s2  ONLINE       0     0     0

    errors: No known data errors
# df -Th
    Filesystem     Type     Size    Used   Avail Capacity  Mounted on
    /dev/mfid0s1a  ufs      496M    275M    182M    60%    /
    devfs          devfs    1.0K    1.0K      0B   100%    /dev
    /dev/mfid0s1e  ufs      496M     12K    456M     0%    /tmp
    /dev/mfid0s1f  ufs      9.2G    1.2G    7.3G    14%    /usr
    /dev/mfid0s1d  ufs      4.8G    766K    4.4G     0%    /var
    expdsk         zfs      229G     23G    207G    10%    /expdsk

# vi /etc/rc.conf
    nfs_server_enable="YES"
    mountd_flags="-r"
    mountd_enable="YES"
    rpcbind_enable="YES"
# vi /etc/exports
    /expdsk -network 192.168.184.0 -mask 255.255.255.192 -mapall=root
# vi /etc/hosts.allow
    rpcbind : 192.168.184.0/255.255.255.192 : allow
# service rpcbind start
# service nfsd start
# service mountd start

# zfs sharenfs=on /expdsk

--- nfs client(CentOS5.5 i386) ---
The vdbench(5.02) is executed on client side(CentOS5.5), kernel panic is occurred on nfs server(freebsd8.1) after while.

# mount -t nfs 192.168.184.xx:/expdsk /mnt

# ./vdbench -f vdb_setting
<<vdb_setting>>
    fsd=fsd1,anchor=/mnt,depth=5,width=3,files=200,sizes=(4k,25,32k,15,256k,20,2m,25,16m,15)
    fwd=fwd1,fsd=fsd1,operation=write,xfersizes=64k,fileio=sequential,fileselect=random,threads=4
    rd=rd1,fwd=fwd1,fwdrate=max,format=on,elapsed=180,interval=10

--- nfs server ---
About 24GB is written, and kernel panic as follows is occurred.
    panic: kmem_malloc(131072)&#65306; kmem_map too small: 1356701696 total allocated
    cpuid = 1
    Uptime: 24m43s
    Cannot dump. Device not defined or unavailable
    Automatic reboot in 15 seconds - press akey on the console to abort

How-To-Repeat: # ./vdbench -f vdb_setting