This is VERY interesting. This machine is a PowerMac 9600 with a 750GX 
accelerator and an ATTO SCSI card, amongst other things, running NetBSD 
2-release.

It's been a VERY busy server lately, serving about 50 requests a second 
and on average 10 to 30 Mbps.

Last night, this is what happened:

trap: pid 0.2146431264 (): kernel MCHK trap @ 0x313dec (SRR1=0x49030)
panic: trap
Begin traceback...
0x004f8d60: at trap+0xec
0x004f8de0: kernel MCHK trap by splx+0x14: srr1=0x49030
             r1=0x4f8ea0 cr=0x80009088 xer=0x20000000 ctr=0
0x004f8ea0: at ADBDevTable+0xfb51a34
0x004f8eb0: at rnd_sample_free+0x48
0x004f8ed0: at rnd_timeout+0x9c
0x004f8f00: at softclock+0x248
0x004f8f40: at hardclock+0x314
0x004f8f70: at decr_intr+0xfc
0x004f8fa0: at trapstart+0xaec
0xd64edcf0: at Idle+0x14
0xd64edd00: at mi_switch+0x194
0xd64edd40: at ltsleep+0x3e0
0xd64edd80: at sys_poll+0x1f8
0xd64eded0: at syscall_plain+0xe0
0xd64edf40: user SC trap #209 by 0x41c434e8: srr1=0xf032
             r1=0xffffe040 cr=0x24008084 xer=0x20000000 ctr=0x41976570
End traceback...
syncing disks... trap: pid 0.2146431264 (): kernel MCHK trap @ 0x266c00 
(SRR1=0x49030)
panic: trap
Begin traceback...
0x004f8680: at trap+0xec
0x004f8700: kernel MCHK trap by pool_get+0x234: srr1=0x49030
             r1=0x4f87c0 cr=0x80084024 xer=0 ctr=0x3179bc
0x004f87c0: at ADBDevTable+0x2b51a34
0x004f87f0: at rnd_sample_allocate_isr+0x38
0x004f8810: at rnd_add_uint32+0x19c
0x004f8840: at sddone+0x80
0x004f8860: at scsipi_complete+0x190
0x004f88a0: at scsipi_done+0x118
0x004f88c0: at esiop_scsicmd_end+0x128
0x004f88e0: at esiop_checkdone+0x288
0x004f8910: at esiop_intr+0x9c
0x004f8960: at do_pending_int+0xc8
0x004f89a0: at splx+0x40
0x004f89b0: at ltsleep+0xc0
0x004f89f0: at drain_output+0x78
0x004f8a20: at softdep_fsync_mountdev+0x7c
0x004f8a40: at ffs_full_fsync+0x360
0x004f8ac0: at ffs_fsync+0x74
0x004f8b80: at ffs_sync+0x15c
0x004f8c50: at sys_sync+0x120
0x004f8c80: at vfs_shutdown+0x60
0x004f8ca0: at cpu_reboot+0x1c0
0x004f8cd0: at panic+0x188
0x004f8d60: at trap+0xec
0x004f8de0: kernel MCHK trap by splx+0x14: srr1=0x49030
             r1=0x4f8ea0 cr=0x80009088 xer=0x20000000 ctr=0
0x004f8ea0: at ADBDevTable+0xfb51a34
0x004f8eb0: at rnd_sample_free+0x48
0x004f8ed0: at rnd_timeout+0x9c
0x004f8f00: at softclock+0x248
0x004f8f40: at hardclock+0x314
0x004f8f70: at decr_intr+0xfc
0x004f8fa0: at trapstart+0xaec
0xd64edcf0: at Idle+0x14
0xd64edd00: at mi_switch+0x194
0xd64edd40: at ltsleep+0x3e0
0xd64edd80: at sys_poll+0x1f8
0xd64eded0: at syscall_plain+0xe0
0xd64edf40: user SC trap #209 by 0x41c434e8: srr1=0xf032
             r1=0xffffe040 cr=0x24008084 xer=0x20000000 ctr=0x41976570
End traceback...
dumpsys: TBD
sd3(esiop1:0:3:0): failed to enqueue polling command, retrying...
sd3(esiop1:0:3:0): failed to enqueue polling command, retrying...
sd3(esiop1:0:3:0): failed to enqueue polling command, retrying...
sd3(esiop1:0:3:0): failed to enqueue polling command, retrying...
sd3(esiop1:0:3:0): failed to enqueue polling command
sd3: cache synchronization failed
sd2(esiop1:0:2:0): failed to enqueue polling command, retrying...
sd2(esiop1:0:2:0): failed to enqueue polling command, retrying...
sd2(esiop1:0:2:0): failed to enqueue polling command, retrying...
sd2(esiop1:0:2:0): failed to enqueue polling command, retrying...
sd2(esiop1:0:2:0): failed to enqueue polling command
sd2: cache synchronization failed
sd1(esiop1:0:1:0): failed to enqueue polling command, retrying...
sd1(esiop1:0:1:0): failed to enqueue polling command, retrying...
sd1(esiop1:0:1:0): failed to enqueue polling command, retrying...
sd1(esiop1:0:1:0): failed to enqueue polling command, retrying...
sd1(esiop1:0:1:0): failed to enqueue polling command
sd1: cache synchronization failed
sd0(esiop1:0:0:0): failed to enqueue polling command, retrying...
sd0(esiop1:0:0:0): failed to enqueue polling command, retrying...
sd0(esiop1:0:0:0): failed to enqueue polling command, retrying...
sd0(esiop1:0:0:0): failed to enqueue polling command, retrying...
sd0(esiop1:0:0:0): failed to enqueue polling command
sd0: cache synchronization failed
rebooting

A panic in a panic! That's new!

Anyone have any ideas?

Thanks,
John