external zfs disk keeps writing

[Tom Evans]

On Wed, Sep 3, 2014 at 2:20 PM, Ronald Klop <ronald-lists at klop.ws> wrote:
> Hello,
>
> I have a disk with ZFS which always writes something every
> 'vfs.zfs.txg.timeout' seconds. By default that is 5 seconds. If I make it 30
> I see writing in gstat every 30 seconds.
> I only do a backup by zfs send | zfs recv hourly on this disk. So I don't
> understand why it still writes something every 5 seconds while I am not
> doing anything to this disk.
>
> How can I debug what is being written every 5 seconds?
>
>
> Some info:
>
> I am running FreeBSD 10-STABLE. The disk is an external disk connected by
> USB.
>
> ugen3.2: <Philips> at usbus3
> umass0: <Philips SPE3030CC, class 0/0, rev 2.00/0.00, addr 2> on usbus3
> umass0:  SCSI over Bulk-Only; quirks = 0x4100
> umass0:4:0:-1: Attached to scbus4
> da0 at umass-sim0 bus 0 scbus4 target 0 lun 0
> da0: <Hitachi HDT725032VLAT80 V54O> Fixed Direct Access SCSI-0 device
> da0: 40.000MB/s transfers
> da0: 305245MB (625142448 512 byte sectors: 255H 63S/T 38913C)
> da0: quirks=0x2<NO_6_BYTE>
>
> Occasionally I have a message like this, but it does not seem to hurt
> anything, so it is probably unrelated.
>
> # bzgrep da0 /var/log/messages*
> /var/log/messages.0.bz2:Sep  2 16:49:45 sjakie kernel:
> (da0:umass-sim0:0:0:0): WRITE(10). CDB: 2a 00 00 00 03 66 00 00 02 00
> /var/log/messages.0.bz2:Sep  2 16:49:45 sjakie kernel:
> (da0:umass-sim0:0:0:0): CAM status: CCB request completed with an error
> /var/log/messages.0.bz2:Sep  2 16:49:45 sjakie kernel:
> (da0:umass-sim0:0:0:0): Retrying command
>
> # zpool status extern
>   pool: extern
>  state: ONLINE
>   scan: scrub repaired 454K in 4h36m with 0 errors on Sat Aug  9 08:53:27
> 2014
> config:
>
>         NAME        STATE     READ WRITE CKSUM
>         extern      ONLINE       0     0     0
>           da0       ONLINE       0     0     0
>
> errors: No known data errors
>
> I just created a zpool on da0 so there is no partition table.
>

zfs set atime=off extern?

Cheers

Tom