ZFS: ZIL device export/import

[Ronald Klop]

On Sat, 13 Apr 2013 20:03:47 +0200, mxb <mxb at alumni.chalmers.se> wrote:

>
> Yes, will this require some additional interactions.
>
> The big question is WHY export/import works fine for L2ARC device  
> (cache), but not for log (ZIL device) ?
>
> Well, I tried to partition and then label (via glabel) slices on both  
> ZIL and L2ARC, the created a new pool with labels.
> Result is the same - L2ARC gets attached upon import, but not ZIL.
> GUID reported by 'zdb' is the same for ZIL-partitions on both HU (as  
> well as for L2ARC). The size of cause is the same.

The L2ARC is considered empty on startup/import. The ZIL might contain  
valuable data after a crash. So your setup is wrong. The ZIL is supposed  
to be one-on-one with the pool. You should move the ZILs to the JBOD. You  
can make a mirror of the ZIL devices to improve failsafe operation by  
redundancy.

Ronald.


> //mxb
>
>
> On 13 apr 2013, at 19:53, Adam Nowacki <nowakpl at platinum.linux.pl> wrote:
>
>> On 2013-04-13 19:33, mxb wrote:
>>>
>>> Hello list,
>>>
>>> I'm currently have 2x Head Units (HU) [FreeBSD 9.1] connected to the  
>>> same JBOD via SAS Expander.
>>> Each HU has separate ZIL and L2ARC devices. Hardware on both HU (inc.  
>>> SSD disks for ZIL/L2ARC) is identical.
>>>
>>> This is basically a HA-setup.
>>>
>>> The I do an 'zpool export tank' on the first HU and do 'zpool import  
>>> tank' on the second one, only L2ARC device appears usable.
>>> Import fails, complaining about ZIL device not present.
>>>
>>> According to the man page zpool(8) ZIL device can be imported and  
>>> exported.
>>>
>>> "… Log devices can be added, replaced, attached, detached, imported and
>>>      exported as part of the larger pool. …".
>>>
>>> Do I miss something here?

Yes.

>>> This feature not implemented yet?
>>> Any way to work around this, except that moving ZIL into JBOD?
>>
>> From the same man page:
>> -m      Enables import with missing log devices.
>>
>> ... but that won't be HA since on unclean shutdown of one the other  
>> won't be able to replay the log and some recent writes (or worse) will  
>> be lost.
>>
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