external zfs disk keeps writing

[Ronald Klop]

On Wed, 03 Sep 2014 15:57:13 +0200, Tom Evans <tevans.uk at googlemail.com>  
wrote:

> 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

Yes, atime is off.

Ronald.