Date: Thu, 18 Aug 2016 09:32:14 +0200 From: InterNetX - Juergen Gotteswinter <juergen.gotteswinter@internetx.com> To: linda@kateley.com, Chris Watson <bsdunix44@gmail.com> Cc: freebsd-fs@freebsd.org Subject: Re: HAST + ZFS + NFS + CARP Message-ID: <7468cc18-85e8-3765-2b2b-a93ef73ca05a@internetx.com> In-Reply-To: <6b866b6e-1ab3-bcc5-151b-653e401742bd@kateley.com> References: <61283600-A41A-4A8A-92F9-7FAFF54DD175@ixsystems.com> <20160704183643.GI41276@mordor.lan> <AE372BF0-02BE-4BF3-9073-A05DB4E7FE34@ixsystems.com> <20160704193131.GJ41276@mordor.lan> <E7D42341-D324-41C7-B03A-2420DA7A7952@sarenet.es> <20160811091016.GI70364@mordor.lan> <1AA52221-9B04-4CF6-97A3-D2C2B330B7F9@sarenet.es> <472bc879-977f-8c4c-c91a-84cc61efcd86@internetx.com> <20160817085413.GE22506@mordor.lan> <465bdec5-45b7-8a1d-d580-329ab6d4881b@internetx.com> <20160817095222.GG22506@mordor.lan> <52d5b687-1351-9ec5-7b67-bfa0be1c8415@kateley.com> <92F4BE3D-E4C1-4E5C-B631-D8F124988A83@gmail.com> <6b866b6e-1ab3-bcc5-151b-653e401742bd@kateley.com>
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Am 17.08.2016 um 20:03 schrieb Linda Kateley:
> I just do consulting so I don't always get to see the end of the
> project. Although we are starting to do more ongoing support so we can
> see the progress..
>
> I have worked with some of the guys from high-availability.com for maybe
> 20 years. RSF-1 is the cluster that is bundled with nexenta. Does work
> beautifully with omni/illumos. The one customer I have running it in
> prod is an isp in south america running openstack and zfs on freebsd as
> iscsi. Big boxes, 90+ drives per frame. If someone would like try it, i
> have some contacts there. Ping me offlist.
no offense, but it sounds a bit like marketing.
here: running nexenta ha setup since several years with one catastrophic
failure due to split brain
>
> You do risk losing data if you batch zfs send. It is very hard to run
> that real time.
depends on how much data changes aka delta size
You have to take the snap then send the snap. Most
> people run in cron, even if it's not in cron, you would want one to
> finish before you started the next.
thats the reason why lock files where invented, tools like zrep handle
that themself via additional zfs properties
or, if one does not trust a single layer
-- snip --
#!/bin/sh
if [ ! -f /var/run/replic ] ; then
touch /var/run/replic
/blah/path/zrep sync all >> /var/log/zfsrepli.log
rm -f /var/run/replic
fi
-- snip --
something like this, simple
If you lose the sending host before
> the receive is complete you won't have a full copy.
if rsf fails, and you end up in split brain you loose way more. been
there, seen that.
With zfs though you
> will probably still have the data on the sending host, however long it
> takes to bring it back up. RSF-1 runs in the zfs stack and send the
> writes to the second system. It's kind of pricey, but actually much less
> expensive than commercial alternatives.
>
> Anytime you run anything sync it adds latency but makes things safer..
not surprising, it all depends on the usecase
> There is also a cool tool I like, called zerto for vmware that sits in
> the hypervisor and sends a sync copy of a write locally and then an
> async remotely. It's pretty cool. Although I haven't run it myself, have
> a bunch of customers running it. I believe it works with proxmox too.
>
> Most people I run into (these days) don't mind losing 5 or even 30
> minutes of data. Small shops.
you talk about minutes, what delta size are we talking here about? why
not using zrep in a loop for example
They usually have a copy somewhere else.
> Or the cost of 5-30 minutes isn't that great. I used work as a
> datacenter architect for sun/oracle with only fortune 500. There losing
> 1 sec could put large companies out of business. I worked with banks and
> exchanges.
again, usecase. i bet 99% on this list are not operating fortune 500
bank filers
They couldn't ever lose a single transaction. Most people
> nowadays do the replication/availability in the application though and
> don't care about underlying hardware, especially disk.
>
>
> On 8/17/16 11:55 AM, Chris Watson wrote:
>> 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@kateley.com
>> <mailto:lkateley@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@perdition.city
>>>>>>>>> <mailto:julien@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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