scsi_synchronize_cache - timeout

[Serge Negodyuck]

System: 

FreeBSD 4.9-PRERELEASE #5: Sun Sep 28 13:06:43 EEST 2003


trm0: <Tekram DC395U/UW/F DC315/U Fast20 Wide SCSI Adapter> port 0xb400-0xb4ff 
mem 0xfeafe000-0xfeafefff irq 10 at device 1.0 on pci3
da0 at trm0 bus 0 target 1 lun 0
da0: <FUJITSU MAP3367NP 0108> Fixed Direct Access SCSI-3 device
da0: 40.000MB/s transfers (20.000MHz, offset 15, 16bit), Tagged Queueing 
Enabled
da0: 35046MB (71775284 512 byte sectors: 255H 63S/T 4467C)

I have a problem with a delay of 5 minutes after command "shutdown -r now"

# shutdown -r now:

 Waiting (max 60 seconds) for system process `vnlru' to stop...stopped
 Waiting (max 60 seconds) for system process `bufdaemon' to stop...stopped
 Waiting (max 60 seconds) for system process `syncer' to stop...stopped
 syncing disks... 7
 done
 Uptime: 42s
// There is delay of exactly 5 minutes at this stage.
 Rebooting...

I did some research using DDB.
During reboot function dashutdown() ( sys/cam/scsi/scsi_da.c:1894 ) is called.
There are the following code:
               scsi_synchronize_cache(&ccb.csio,
                                       /*retries*/1,
                                       /*cbfcnp*/dadone,
                                       MSG_SIMPLE_Q_TAG,
                                       /*begin_lba*/0, /* whole disk */
                                       /*lb_count*/0,
                                       SSD_FULL_SIZE,
                                       5 * 60 * 1000);

                xpt_polled_action(&ccb);

The problem is that xpt_polled_action() waits 5 minutes. And never returns 
before 5 minutes elapsed.

So, questions are: 
- Is this a problem of SCSI controller or hard drive?
- Is it a good idea to make this delay tunable in kernel config?
- Will I have troubles if I change this delay to 20 seconds for example?
- How can I help to fix this problem?