What does ZFS write when nothing should write there?

[Attila Nagy]

On 01/10/14 14:29, Dmitry Morozovsky wrote:
> On Fri, 10 Jan 2014, Steven Hartland wrote:
>
>>>>> I've created 6 zpools, each of them with zpool create -m /data/A dataA
>>>>> mirror
>>>>> daX daY.
>>>>> The machine has nothing running except sshd and my shell.
>>>>>
>>>>> Yet, I see this in gstat:
>>>> [snip]
>>>>
>>>>>       0     88      0      0    0.0     82    573    4.1 9.0  da5
>>>>>       0     89      0      0    0.0     83    573    4.8 9.8  da6
>>>>>       0     87      0      0    0.0     81    573    2.6 5.7  da9
>>>>>       0     89      0      0    0.0     84    573    3.0 6.7  da10
>>>> Did you turn off atime?
>>>>
>>> No, but how does it matter?
>>> The process list is the following: init, getty, sshd, csh and the pool is
>>> completely empty.
>> With atime on each time you access a file it will update its "atime"
>> hence causing writes.
>>
>> We use atime=off at the pool level on all machines to avoid that
>> zfs set atime=off <pool>
> BTW, it seems that ZFS updates atime of some inodes (root one?) on every kernel
> update thread invocation even when completely empty -- is it correct behaviour?
>
Because there are no files, it must (?) be the root. But at this frequency?