HAST + ZFS + NFS + CARP

Wed Aug 17 16:55:32 UTC 2016

Of course, if you are willing to accept some amount of data loss that opens up a lot more options. :)

Some may find that acceptable though. Like turning off fsync with PostgreSQL to get much higher throughput. As little no as you are made *very* aware of the risks. 

It's good to have input in this thread from one with more experience with RSF-1 than the rest of us. You confirm what others have that said about RSF-1, that it's stable and works well. What were you deploying it on?

Chris

Sent from my iPhone 5

> On Aug 17, 2016, at 11:18 AM, Linda Kateley <lkateley at kateley.com> wrote:
> 
> The question I always ask, as an architect, is "can you lose 1 minute worth of data?" If you can, then batched replication is perfect. If you can't.. then HA. Every place I have positioned it, rsf-1 has worked extremely well. If i remember right, it works at the dmu. I would suggest try it. They have been trying to have a full freebsd solution, I have several customers running it well.
> 
> linda
> 
> 
>> On 8/17/16 4:52 AM, Julien Cigar wrote:
>>> On Wed, Aug 17, 2016 at 11:05:46AM +0200, InterNetX - Juergen Gotteswinter wrote:
>>> 
>>>> Am 17.08.2016 um 10:54 schrieb Julien Cigar:
>>>>> On Wed, Aug 17, 2016 at 09:25:30AM +0200, InterNetX - Juergen Gotteswinter wrote:
>>>>> 
>>>>> Am 11.08.2016 um 11:24 schrieb Borja Marcos:
>>>>>>> On 11 Aug 2016, at 11:10, Julien Cigar <julien at perdition.city> wrote:
>>>>>>> 
>>>>>>> As I said in a previous post I tested the zfs send/receive approach (with
>>>>>>> zrep) and it works (more or less) perfectly.. so I concur in all what you
>>>>>>> said, especially about off-site replicate and synchronous replication.
>>>>>>> 
>>>>>>> Out of curiosity I'm also testing a ZFS + iSCSI + CARP at the moment,
>>>>>>> I'm in the early tests, haven't done any heavy writes yet, but ATM it
>>>>>>> works as expected, I havent' managed to corrupt the zpool.
>>>>>> I must be too old school, but I don’t quite like the idea of using an essentially unreliable transport
>>>>>> (Ethernet) for low-level filesystem operations.
>>>>>> 
>>>>>> In case something went wrong, that approach could risk corrupting a pool. Although, frankly,
>>>>>> ZFS is extremely resilient. One of mine even survived a SAS HBA problem that caused some
>>>>>> silent corruption.
>>>>> try dual split import :D i mean, zpool -f import on 2 machines hooked up
>>>>> to the same disk chassis.
>>>> Yes this is the first thing on the list to avoid .. :)
>>>> 
>>>> I'm still busy to test the whole setup here, including the
>>>> MASTER -> BACKUP failover script (CARP), but I think you can prevent
>>>> that thanks to:
>>>> 
>>>> - As long as ctld is running on the BACKUP the disks are locked
>>>> and you can't import the pool (even with -f) for ex (filer2 is the
>>>> BACKUP):
>>>> https://gist.github.com/silenius/f9536e081d473ba4fddd50f59c56b58f
>>>> 
>>>> - The shared pool should not be mounted at boot, and you should ensure
>>>> that the failover script is not executed during boot time too: this is
>>>> to handle the case wherein both machines turn off and/or re-ignite at
>>>> the same time. Indeed, the CARP interface can "flip" it's status if both
>>>> machines are powered on at the same time, for ex:
>>>> https://gist.github.com/silenius/344c3e998a1889f988fdfc3ceba57aaf and
>>>> you will have a split-brain scenario
>>>> 
>>>> - Sometimes you'll need to reboot the MASTER for some $reasons
>>>> (freebsd-update, etc) and the MASTER -> BACKUP switch should not
>>>> happen, this can be handled with a trigger file or something like that
>>>> 
>>>> - I've still have to check if the order is OK, but I think that as long
>>>> as you shutdown the replication interface and that you adapt the
>>>> advskew (including the config file) of the CARP interface before the
>>>> zpool import -f in the failover script you can be relatively confident
>>>> that nothing will be written on the iSCSI targets
>>>> 
>>>> - A zpool scrub should be run at regular intervals
>>>> 
>>>> This is my MASTER -> BACKUP CARP script ATM
>>>> https://gist.github.com/silenius/7f6ee8030eb6b923affb655a259bfef7
>>>> 
>>>> Julien
>>>> 
>>> 100€ question without detailed looking at that script. yes from a first
>>> view its super simple, but: why are solutions like rsf-1 such more
>>> powerful / featurerich. Theres a reason for, which is that they try to
>>> cover every possible situation (which makes more than sense for this).
>> I've never used "rsf-1" so I can't say much more about it, but I have
>> no doubts about it's ability to handle "complex situations", where
>> multiple nodes / networks are involved.
>> 
>>> That script works for sure, within very limited cases imho
>>> 
>>>>> kaboom, really ugly kaboom. thats what is very likely to happen sooner
>>>>> or later especially when it comes to homegrown automatism solutions.
>>>>> even the commercial parts where much more time/work goes into such
>>>>> solutions fail in a regular manner
>>>>> 
>>>>>> The advantage of ZFS send/receive of datasets is, however, that you can consider it
>>>>>> essentially atomic. A transport corruption should not cause trouble (apart from a failed
>>>>>> "zfs receive") and with snapshot retention you can even roll back. You can’t roll back
>>>>>> zpool replications :)
>>>>>> 
>>>>>> ZFS receive does a lot of sanity checks as well. As long as your zfs receive doesn’t involve a rollback
>>>>>> to the latest snapshot, it won’t destroy anything by mistake. Just make sure that your replica datasets
>>>>>> aren’t mounted and zfs receive won’t complain.
>>>>>> 
>>>>>> 
>>>>>> Cheers,
>>>>>> 
>>>>>> 
>>>>>> 
>>>>>> 
>>>>>> Borja.
>>>>>> 
>>>>>> 
>>>>>> 
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