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Snapshot

Article ID: 159
Last updated: 30 Mar, 2010
Views: 4501
Snapshot Rating: 10.0000 / 10
Votes: 1
Posted: 25 Feb, 2009
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Updated: 30 Mar, 2010
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Question:

I see there is manual mode and a schedule for snapshots.

But for the schedule there is a range of time - how does this work?

I check the manual and the on-line help but it is not adding any
information.

For example I thought a snap shot was a point in time not a range of
time.

If I put a start of 06:00 & and end of 18:00 what does that mean - start
a snapshot @ 06:00 or for the only whole day or ???

Also, I see mention on other systems of how many snapshots to keep,
certainly important when sizing a snapshot volume, how does this system
control the number of snapshots that are retained?

Answer:

If you have a start time of 06:00 & and end of 18:00 what does this mean?

What this means is that the Snapshot will start at 6am and will end at 4pm. The Snapshot
only takes less than a min. then allows you to access the Snapshot until 4pm or until the
next scheduled. The Snapshot does not continue for the whole day up to 4pm. This can
tested by creating a Snapshot to see how the point in time is used.

I have included additional information that might be of use to you.

Q. How many Snapshots can I create?
A. You can create up to 10 active snapshots per volume and 20 per the
whole system. This in reference to what is currently active, you can
create many Snapshots but only the amount of active Snapshots.

Snapshot will make a record of all files that have been modified. Snapshot preserves the
image of the data as it is  when the Snapshot is first run.
So this is a point in time Snapshot, we use COW "Copy on Write".

Q. What happens if my changes is larger then the Snapshot volume?
A. If the data copied to the snapshot is larger than the snapshot volume it becomes
deactivated and all data stored on it is lost but not the actual data.
We recommend to have enough space for the Snapshot to avoid this issue.

Q. What size should be the size of a Snapshot and what of the performance?
A. Large number of snapshots will generate very high load which will slow the performance.
Open-e recommends 10-12% (generally) of the volume size for a snapshots, or 3 times the
amount of changes that will be generated.

Snapshot depends on the changes, if volume size is 100GB and the daily changes of the data
is 30G, then snapshot needs to be more than 30G set for daily snap.

Q. If Snapshot get filled will it affect or corrupt the Logical Volume?
No, just expand the snapshot then it will be fine – that is you do this before the
scheduled snapshot.

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