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Date:      Thu, 17 May 2012 13:32:28 +0200
From:      Adam Nowacki <nowakpl@platinum.linux.pl>
To:        freebsd-fs@freebsd.org
Subject:   Re: Mirror of Raidz for data reliability
Message-ID:  <4FB4E1CC.8030501@platinum.linux.pl>
In-Reply-To: <CA%2BdUSyraV54L_j01gQaWYCsmNJBOt4-j4OayxiiRfMFO4vJLqg@mail.gmail.com>
References:  <CAOfEmZh8v5xbQqkJJ7ZKkan7Ho0FPNrXJ95S1WRpioDXVG6P7w@mail.gmail.com>	<20120515102206.GA53750@psconsult.nl>	<CAOfEmZiTkr9Xcj6J4FRBd4FzL1ztgEpytSAUc=wZ8DBJtXsH%2Bg@mail.gmail.com>	<CA%2BdUSyrG-RFFjchEYfovbvORVBZNHes9r9MhhGG1d568cO-CwA@mail.gmail.com>	<CAOfEmZhtxvNM3kiK5mvTZCxzkTiVWKt97yAudfaxFCnjbANQ0g@mail.gmail.com>	<CA%2BdUSyppT%2Bngjn9UXBVW1K0eDa93OB00Rd=TX31brwmAaxNy8w@mail.gmail.com> <CA%2BdUSyraV54L_j01gQaWYCsmNJBOt4-j4OayxiiRfMFO4vJLqg@mail.gmail.com>

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My understanding of this setup is:
- there are 2 chasis housing disks, each with a 2 port SAS expander,
- there are 2 servers, each with a 2 port SAS HBA (1st port connected to 
1st SAS expander, 2nd port connected to 2nd SAS expander).

On 2012-05-17 13:17, George Kontostanos wrote:
> On Thu, May 17, 2012 at 1:52 PM, George Kontostanos
> <gkontos.mail@gmail.com>  wrote:
>> On Thu, May 17, 2012 at 3:29 AM, Marcelo Araujo<araujobsdport@gmail.com>  wrote:
>>> George,
>>>
>>>>
>>>> If you have 2 machines then your best bet would be HAST.
>>>
>>>
>>> So, why use ETHERNET if my Machine can see both JBOD?
>>
>> I was under the impression that you are talking about 2 different
>> physical machines.
>>
>>>> If you are worried about data replication you can always use lagg with
>>>> 2 or more interfaces.
>>>
>>>
>>> It is different than data replication. It is data protection.
>>
>> Storing the same data in 2 different locations is data protection.
>>
>> Regards
>>
>
> Ok, after reading more carefully your first post I realized what you
> are trying to do.
>
> 2 Machines, 2 different controllers. Yet interconnected. So, in a way
> both machines would be able to see both controllers.
>
> This is very interesting but there are some implications.
>
> 1) Suppose you manage to create a mirror consisted by drives on those
> different controllers. If you reboot machine #1 machine#2 might panic.
> It is not like loosing a drive, here we are loosing a controller.
>
> 2) Both machines have to be online and the pool has to be mounted
> readonly on the standby! You don't want both of them to accidentally
> write at the same pool.
>
> 3) HAST requires tcp to work therefore it is a no go. HAST also works
> in the vdev level. Therefore the resources should not be online on the
> standby server.
>
> Good luck, this is certainly very interesting.
>




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