Date: Sun, 9 Mar 2008 15:25:26 +1000 From: Duncan Young <duncan.young@pobox.com> To: freebsd-current@freebsd.org Subject: write cache on usb disks and zfs Message-ID: <200803091525.27311.duncan.young@pobox.com>
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Hi all I am having a few problems with external usb2 disk and write caching. I have some caddies which allow write caching (seen and editable via camcontrol) and others which automatically disable it. i.e. #camcontrol modepage da2 -m 8 IC: 0 ABPF: 0 CAP: 0 DISC: 0 SIZE: 0 WCE: 0 MF: 0 RCD: 0 Demand Retention Priority: 0 Write Retention Priority: 0 Disable Pre-fetch Transfer Length: 0 Minimum Pre-fetch: 0 Maximum Pre-fetch: 0 Maximum Pre-fetch Ceiling: 0 and #camcontrol modepage da2 -m 8 -e camcontrol: no editable entries 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? Duncan
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