Mirror of Raidz for data reliability

[Marcelo Araujo]

Hello Adam,

Well, in my understand it would be not the same.
Because it will works as a stripe, and OK we have 2 copies of each striped
data between both raidz, however I don't have a mirror for every each disk
in the pool, so no data protection. Also I could scale with more JBOD or
Machines till 3 times, because zfs set copies support till 3 copies.

In case, I use something like:
zpool create tank raidz da0 da1 raidz da2 da3 raidz da4 da5 raidz da6 da7

I don't have set copies=4, but in the previous email that I sent, you have
no limit to set more mirrors.


What do you think?

Best Regards,
- Araujo


2012/5/14 Adam Nowacki <nowakpl at platinum.linux.pl>

> Wouldn't this accomplish the same?
> zpool create tank raidz da0 da1 da2 raidz da3 da4 da5
> zfs set copies=2 tank
>
>
> On 2012-05-13 19:35, Marcelo Araujo wrote:
>
>> Hi All,
>>
>> Me and a co-work are working in a new feature for ZFS, we have 2 Machines
>> and 2 JBOD, every Machine are connected on those JBOD via SAS and we are
>> trying to make a fail-over server. Currently every each Machine has two
>> SAS
>> cables, each one connected in both JBOD.
>>
>> We have worked last week to figure out, how we could make the data be
>> always alive in case one JBOD dies, and let me show you my console output
>> ;):
>>
>> controllerA# zpool status -v araujo
>>   pool: araujo
>>  state: ONLINE
>>  scan: resilvered 57K in 0h0m with 0 errors on Sat May 12 14:32:29 2012
>> config:
>>
>>         NAME          STATE     READ WRITE CKSUM
>>         araujo        ONLINE       0     0     0
>>           raidz1-0    ONLINE       0     0     0
>>             mirror-0  ONLINE       0     0     0
>>               da0     ONLINE       0     0     0
>>               da3     ONLINE       0     0     0
>>             mirror-1  ONLINE       0     0     0
>>               da1     ONLINE       0     0     0
>>               da4     ONLINE       0     0     0
>>             mirror-2  ONLINE       0     0     0
>>               da2     ONLINE       0     0     0
>>               da5     ONLINE       0     0     0
>>
>>
>> What I have is: A file system called "araujo" created using raidz with 3
>> disks, than, I can attache new disks to create a mirror for every disk
>> that
>> is part of the raidz, with this case, if one of my JBOD fail, my raidz
>> will
>> still alive, also I can scale with more JBOD to make sure that my data
>> will
>> be always alive.
>>
>> Currently is possible to do the solution above, just comment few lines of
>> code, but our plan is bring something new like:
>> root# zpool create tank raidzm da0 da1 da2 da3 da4 da5
>>
>> Where da0 da1 da2 will be raidz and da3 da4 da5 will be mirror of da0 da1
>> da2. In this case, if da0 da1 or da2 fail, we have the mirror and the
>> raidz
>> will still works.
>>
>> I’m wondering if there is any other elegant solution for this case, HAST
>> could be an option, but I don’t want use ETHERNET to sync JBOD, and in the
>> case above, it is faster to sync any hard driver more less locally.
>>
>>
>> Best Regards,
>>
>
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-- 
Marcelo Araujo
araujo at FreeBSD.org