write cache on usb disks and zfs
duncan.young at pobox.com
Sat Mar 8 21:41:02 PST 2008
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
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
#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?
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