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SnapMirror Bi-directional possible?
Just wanted to do a quick sanity check, is there any way to have SnapMirror replication go both directions between sites? We are running cDOT 9.x at both locations.

I came across some older posts (several years ago) that seem to indicate that bi-directional snapmirror would not be possible. Just wondering if this might have changed with cDOT 9.x capabilities?

Thanks,
Eric
Re: SnapMirror Bi-directional possible? [ In reply to ]
Hi,

On 2018-07-24 20:48, Eric Peng wrote:
> Just wanted to do a quick sanity check, is there any way to have
> SnapMirror replication go both directions between sites?  We are running
> cDOT 9.x at both locations.

Depends on what you mean exactly. For the same volume? No, of course
not. For different volumes? Sure, works just fine, as you'd expect.
You're better off using XDP relationships, though, due to ONTAP version
inter-dependencies.

> I came across some older posts (several years ago) that seem to indicate
> that bi-directional snapmirror would not be possible.  Just wondering if
> this might have changed with cDOT 9.x capabilities?
AFAIK this has always worked, even back in the DOT7G days. But I only
really started using cDOT with 8.3, so 8.0-8.2 might have had limitations.

Regards
Oliver
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RE: SnapMirror Bi-directional possible? [ In reply to ]
Hmm, I do it in 7m, seems weird that you would not be able to do that in cm. To be clear, we are talking about different volumes obviously, right? Site1_volume ----> mirror_Site1_volume and site2_volume ----> mirror_site2_volume

--Jordan

-----Original Message-----
From: toasters-bounces@teaparty.net [mailto:toasters-bounces@teaparty.net] On Behalf Of Oliver Brakmann
Sent: Tuesday, July 24, 2018 3:17 PM
To: toasters@teaparty.net
Subject: Re: SnapMirror Bi-directional possible?

Hi,

On 2018-07-24 20:48, Eric Peng wrote:
> Just wanted to do a quick sanity check, is there any way to have
> SnapMirror replication go both directions between sites?  We are
> running cDOT 9.x at both locations.

Depends on what you mean exactly. For the same volume? No, of course not. For different volumes? Sure, works just fine, as you'd expect.
You're better off using XDP relationships, though, due to ONTAP version inter-dependencies.

> I came across some older posts (several years ago) that seem to
> indicate that bi-directional snapmirror would not be possible.  Just
> wondering if this might have changed with cDOT 9.x capabilities?
AFAIK this has always worked, even back in the DOT7G days. But I only really started using cDOT with 8.3, so 8.0-8.2 might have had limitations.

Regards
Oliver
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Re: SnapMirror Bi-directional possible? [ In reply to ]
On Tue, Jul 24, 2018 at 12:24 PM, Jordan Slingerland
<Jordan.Slingerland@independenthealth.com> wrote:
> Hmm, I do it in 7m, seems weird that you would not be able to do that in cm. To be clear, we are talking about different volumes obviously, right? Site1_volume ----> mirror_Site1_volume and site2_volume ----> mirror_site2_volume

I think the OP wants to do bi-drectional vaults with the *same* volume pair.

You can't do that. you sure can do vaults in various directions with
different volume pairs,
which is a handy way to protect data across your various sites.

-skottie

>
> --Jordan
>
> -----Original Message-----
> From: toasters-bounces@teaparty.net [mailto:toasters-bounces@teaparty.net] On Behalf Of Oliver Brakmann
> Sent: Tuesday, July 24, 2018 3:17 PM
> To: toasters@teaparty.net
> Subject: Re: SnapMirror Bi-directional possible?
>
> Hi,
>
> On 2018-07-24 20:48, Eric Peng wrote:
>> Just wanted to do a quick sanity check, is there any way to have
>> SnapMirror replication go both directions between sites? We are
>> running cDOT 9.x at both locations.
>
> Depends on what you mean exactly. For the same volume? No, of course not. For different volumes? Sure, works just fine, as you'd expect.
> You're better off using XDP relationships, though, due to ONTAP version inter-dependencies.
>
>> I came across some older posts (several years ago) that seem to
>> indicate that bi-directional snapmirror would not be possible. Just
>> wondering if this might have changed with cDOT 9.x capabilities?
> AFAIK this has always worked, even back in the DOT7G days. But I only really started using cDOT with 8.3, so 8.0-8.2 might have had limitations.
>
> Regards
> Oliver
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Re: SnapMirror Bi-directional possible? [ In reply to ]
You could look at metrocluster, potentially

Sent from my mobile phone

> On Jul 24, 2018, at 5:53 PM, Eric Peng <epeng@esri.com> wrote:
>
> Thanks all, for confirming that bi-directional SnapMirror on the *same* volume is not possible. We're still in the requirements gathering/planning part of the project, so we have some time to figure this out. This would be for keeping user profiles in sync between 2 different sites. I may take a look at that PeerSync software.
>
> Eric
>
> -----Original Message-----
> From: toasters-bounces@teaparty.net [mailto:toasters-bounces@teaparty.net] On Behalf Of Michael Bergman
> Sent: Tuesday, July 24, 2018 3:07 PM
> To: Toasters <toasters@teaparty.net>
> Subject: Re: SnapMirror Bi-directional possible?
>
>> On 2018-07-24 23:35, Scott M Gelb via Toasters wrote:
>> For the same data set, bi-directional, you might want to POC Peer Software.
>> They PeerSync bi-directional and also have PeerLink which locks files
>> on either side while keeping in sync. FPOLICY is used for real time
>> event notification without file scans.
>
> Locks files... Well, if you can live with that, then *maybe* it's viable.
>
> But cumbersome and slow. Now, in many use cases w.r.t. NFS (which is what is used by the Applications to *do* something with that data right?) the problems which such locking incur can be devastating in practice. If it's just some ppl browsing files manually, then sure -- go ahead.
>
> But with many heavy application systems it's just not acceptable. So the whole things falls over in any case. This might not be detectable in a PoC; race conditions. It's a bogmire of ifs and buts.
>
> In a way normal one-directional SM also "locks" (or rather, makes
> not-available) files and dirs in the RO target volume. In a certain way. So if you run applications intensely on the RO copy (target FlexVol) via NFS there is always a short moment when inodes are shifted at the updates. This is absolutely unavoidable, but what will happen to the App is then 'Stale NFS file handle'. Ka-boom. So then you go into the complexity of trying to asynchronously time the app chain to not run (in certain ways at least) at the exact second(s) this shift inside the inode structure happens.
>
> And then you give up. Been there, done that.
>
> /M
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Re: SnapMirror Bi-directional possible? [ In reply to ]
You can also look at somthing like DFS or a global name space like panzura. I believe they can do multiple copies but have some hardware requirements.



On July 24, 2018 at 4:40:09 PM PDT, Mike Gossett <cmgossett@gmail.com> wrote:
You could look at metrocluster, potentially

Sent from my mobile phone

> On Jul 24, 2018, at 5:53 PM, Eric Peng <epeng@esri.com> wrote:
>
> Thanks all, for confirming that bi-directional SnapMirror on the *same* volume is not possible. We're still in the requirements gathering/planning part of the project, so we have some time to figure this out. This would be for keeping user profiles in sync between 2 different sites. I may take a look at that PeerSync software.
>
> Eric
>
> -----Original Message-----
> From: toasters-bounces@teaparty.net [mailto:toasters-bounces@teaparty.net] On Behalf Of Michael Bergman
> Sent: Tuesday, July 24, 2018 3:07 PM
> To: Toasters <toasters@teaparty.net>
> Subject: Re: SnapMirror Bi-directional possible?
>
>> On 2018-07-24 23:35, Scott M Gelb via Toasters wrote:
>> For the same data set, bi-directional, you might want to POC Peer Software.
>> They PeerSync bi-directional and also have PeerLink which locks files
>> on either side while keeping in sync. FPOLICY is used for real time
>> event notification without file scans.
>
> Locks files... Well, if you can live with that, then *maybe* it's viable.
>
> But cumbersome and slow. Now, in many use cases w.r.t. NFS (which is what is used by the Applications to *do* something with that data right?) the problems which such locking incur can be devastating in practice. If it's just some ppl browsing files manually, then sure -- go ahead.
>
> But with many heavy application systems it's just not acceptable. So the whole things falls over in any case. This might not be detectable in a PoC; race conditions. It's a bogmire of ifs and buts.
>
> In a way normal one-directional SM also "locks" (or rather, makes
> not-available) files and dirs in the RO target volume. In a certain way. So if you run applications intensely on the RO copy (target FlexVol) via NFS there is always a short moment when inodes are shifted at the updates. This is absolutely unavoidable, but what will happen to the App is then 'Stale NFS file handle'. Ka-boom. So then you go into the complexity of trying to asynchronously time the app chain to not run (in certain ways at least) at the exact second(s) this shift inside the inode structure happens.
>
> And then you give up. Been there, done that.
>
> /M
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RE: SnapMirror Bi-directional possible? [ In reply to ]
>>>>> "Eric" == Eric Peng <epeng@esri.com> writes:

Eric> Thanks all, for confirming that bi-directional SnapMirror on the
Eric> *same* volume is not possible. We're still in the requirements
Eric> gathering/planning part of the project, so we have some time to
Eric> figure this out. This would be for keeping user profiles in
Eric> sync between 2 different sites. I may take a look at that
Eric> PeerSync software.

Hmm... if a user is logged into one site, will they be logged into
another site at the same time? Maybe you just do robocopy once an
hour to bring them all in sync, with last written winning?

Or, since profiles should be small, can you simply share the CIFS
share holding the profiles across the WAN from the main site to the
remote site?

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