Capacity; Retention Policies; Snapshot Retention Policy And Maximum Number Of Retained Snapshots - HP StorageWorks P4000 User Manual

4. Track the time required to complete the second remote snapshot.
NOTE:
This is the minimum amount of time that you should allow between scheduled copies.
5. Check the remote bandwidth setting for the other management group by using the Edit
Management Group command. This setting affects the time required to copy a remote snapshot.

Capacity

Does the cluster that contains the remote volume have sufficient space to accommodate scheduled
snapshots?
If the cluster does not have sufficient space available, the remote snapshot appears in the CMC and
flashes red. On the Details tab of the remote snapshot, the status message displayed is Read only,
not enough space in cluster to start copy.

Retention policies

How long do you want to retain the primary snapshots? The remote snapshots? You can set different
retention policies for the primary and remote snapshots. For example, you can choose to retain two
primary snapshots and five remote snapshots. The number of snapshots retained refers to completed
snapshots. Take the following characteristics of scheduled remote snapshots into account when planning
retention policies.
The SAN/iQ software never deletes the last fully synchronized remote snapshot.
Under some circumstances, such as unpredictable network speeds or varying snapshot size, a
scheduled remote snapshot may create primary snapshots so frequently that the remote copy
process cannot keep up with them. The retention policies for scheduled remote snapshots ensure
that such factors do not cause primary and remote snapshots to become unsynchronized. Regardless
of the retention policy defined for scheduled remote snapshots, up to two additional snapshots
may be retained by the system at any given time. These two additional snapshots include the
snapshot that is in the process of being copied and the last fully synchronized snapshot. A fully
synchronized snapshot is one that has completed copying so that the remote snapshot matches
its corresponding primary snapshot.
Up to two additional snapshots may be retained at any given time.
Because the SAN/iQ software never deletes the last fully synchronized snapshot, a remote copy
schedule may retain n+2 copies for a retention policy of n (the currently copying remote snapshot
plus the last fully synchronized snapshot). Using the example above, if you have a retention policy
for your remote copy schedule of two primary and five remote snapshots, the software may retain
up to four primary and seven remote snapshots for a period of time.
the maximum retained snapshots with respect to a specific retention policy.
Table 3 Snapshot retention policy and maximum number of retained snapshots
Scheduled remote snapshot retention policy
n of primary snapshots x of remote snapshots
n of hours for primary snapshots x of hours for remote
snapshots
14 Understanding and planning Remote Copy
Table 3
Maximum number of snapshots retained
n + 2 of primary snapshots x + 2 of remote snapshots
n + 2 primary snapshots older than nx + 2 remote
snapshots older than x
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