Re: gmirror + ZFS issues

On 16/05/2014 09:36, Karl Denninger wrote:
>
> On 5/16/2014 8:23 AM, Nicolas Haller wrote:
>> Hello,
>>
>> I've got a new server and I installed FreeBSD 10 on it. I have a
>> problem to create a new zfs pool. The command stalls on IO wait (D
>> state / zio->io_cv).
>>
>> The device for the pool is a 1.7T partition (index 4) of a gmirror
>> device.
> Why?
>
> ZFS provides its own mirroring and it is superior, as it checksums each
> block and thus does not rely on the drive returning an error to detect
> problems.  It can also rewrite a bad block (assuming the problem is
> transient) and scrub also relies on independent components.
>
> You're destroying the data integrity advantage that ZFS gives you by
> using a gmirror under it.  Stop doing that and see if your problem
> disappears.
>
> (In other words it sounds like the problem is real but you shouldn't be
> doing that anyway, so it also shouldn't bite you.)
>

Yes you're right but I have two disks on this server which host my 
non-zfs root fs. The first 98G partition you show on "gpart show" output 
is my UFS root fs and I want it mirrored.

As I'm not sure it's a good idea to mix gmirror and ZFS mirror on the 
same drives (What do you think about this?), I let gmirror handle the 
mirror thing.

So, yes, I drop the data integrity advantage, but I keep the flexibility 
given by pools/datasets, send/receive, compression...
It's not so bad :-)

-- 
Nicolas Haller
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