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AMMSCL
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SnapShotIQ Function behind the Scenes question

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Customer has 2 different snapshot policies running against the same file system path.

The path is /ifs/data/imagescpacs

there is a hourly snapshot and a daily snapshot policy running against the above mentioned path.

During a single 24 hour window (Oct 13th 11pm till Oct 14th 11pm); the hourly snapshots have several snaps that are 19GB in size each.

The total Snapshot space for the hourly policy during the 24 hour window is approximately 160GB in size.

The Daily Snapshot space used for the same 24 hour period is 53.8MB in size.

The clarification that I am attempting to find out is does the Daily Snapshot base changes on the previously saved Daily Snapshot? i.e. Compare this current exact time (Oct 14th 11pm) vs the previous Daily Oct 13th 11pm Snapshot

or

Does the Daily Snapshot get compared to the last Snapshot (no matter the policy) that was taken against the file system path (/ifs/data/imagescpacs)? i.e. Daily now running at this exact time of Oct 14th 11pm gets compared the last Hourly Snapshot taken at Oct 14th 11pm (this is based on the hourly policy running before the daily policy)

I would have thought the SnapShot Funcition would be the 1st example and the daily would be some what close in size of the combined Hourlys. I am just trying to get some clarification.

Thank You

Ray Sissons

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AMMSCL
1 Copper

Re: SnapShotIQ Function behind the Scenes question

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I got my answer.

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AMMSCL
1 Copper

Re: SnapShotIQ Function behind the Scenes question

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I got my answer.

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Peter_Sero
3 Zinc

Re: SnapShotIQ Function behind the Scenes question

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It works in the second way. And if you take snapshots manually they also become part of the sequence.

This makes snapshots very space-efficient.

However there's one important thing to note:

The deletion of Snapshots (for one given path) always should start with the oldest one,

and  then proceed to newer ones in the order they were taken. Out-of-order deletions

take more time (file system operations) and should be avoided in general, unless the

overhead is understood and can be accepted.

The daily policy most likely has a longer retention time than the hourly policy.

That would break the general rule, as the hourly snaps are deleted

before the older daily snaps. Observe the SnapshotDelete jobs carefully to see

wether they complete within reasonable amount of time; this might increase

slowly to unexpected periods of activity with the cluster getting more filled.

Cheers

-- Peter