Re: write cache on usb disks and zfs

Hi,

On 9 Mar 2008, at 06:25, Duncan Young wrote:

> I am trying to use the USB drives for backup and would like to use  
> zfs on
> them, but the problem I have is with the cache disabled, I get lots of
>
> kernel: (da2:umass-sim0:0:0:0): SYNCHRONIZE CACHE. CDB: 35 0 0 0 0 0  
> 0 0 0 0
> kernel: (da2:umass-sim0:0:0:0): CAM Status: SCSI Status Error
> kernel: (da2:umass-sim0:0:0:0): SCSI Status: Check Condition
> kernel: (da2:umass-sim0:0:0:0): ILLEGAL REQUEST asc:20,0
> kernel: (da2:umass-sim0:0:0:0): Invalid command operation code
> kernel: (da2:umass-sim0:0:0:0): Unretryable error
>
> errors in /var/log/messages.
>
> I am assuming that the error messages are harmless, but it would be  
> nice for
> zfs to pay attention and not continually issue the commands.  Is  
> there a way
> to do this?

I had exactly the same problem (on 7-stable) and have added a quirk  
for this particular drive to scsi_da.c. In my case the drive became  
unresponsive for a few seconds, so the transfer rate was very low.

Works fine so far with the quirk. I have filed a PR where you can see  
my changes: http://www.freebsd.org/cgi/query-pr.cgi?pr=121474

Ben