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FR and space guaruntee on a SnapMirror volume

marcconeley
7,130 Views

Hi,

Is it possible to set space guarantee to NONE on a snapmirror destination volume which has Fractional Reserve set to less than 100%??

Originally we had an SQL vol with FR set to 100% which we snapmirrored. The destination vol was not thin provisioned, and therefore every time we resize the source vol we have to also resize the destination.

However, now we have reduced the FR to 50% and enabled snap autodelete and vol autogrow - sounds good and works fine. But the problem is that if the vol autogrows, the source will be bigger than the target and snapmirror fails. My way around this was to set space guarantee to NONE on the target volume and thin provision it (so if the source autogrows, the target won't care as long as there is space in the agg).

I am having trouble configuring this though as I see that space guarantee apparently cannot be set to NONE if the FR is less than 100%??? (and when I try and do this on the destination volume it gives an error). Also, it seems that the FR setting gets copied from the source and has to be the same at both ends - so I can't change FR on the target to 100% without also changing it on the source?!

Anyone got any suggestions on the best way to manage this?

Or does the vol autogrow setting that we enabled on the source also mean that the snapmirror target will also autogrow automatically and therefore I don't have to worry about thin provisioning it? (I can't believe this would happen).

Help as always much appreciated!

Marc

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radek_kubka
6,405 Views

Therefore in reducing the FR% to get better disk utilization on my filers, I am actually only saving space on my source filer but taking up more space on my destination filer?

Don't worry, it won't happen.

SnapMirror is block-for-block, so when you replicate your destination won't get bigger than the source. Again, two facts:

- when you break the mirror, the destination will automatically inherit all the settings from the source

- when you set vol guaratee to none, FR is nominally fixed to 100%, but in reality everything behaves like FR is set to 0% (odd, but this is how it looks like)

Regards,

Radek

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