Capacity, Retention policies – HP StoreVirtual 4000 Storage User Manual
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1.
Create a remote snapshot of the primary volume.
2.
Wait for the copy to finish.
3.
Create another remote snapshot of the primary volume.
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 LeftHand OS 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 LeftHand OS 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.
shows the maximum retained snapshots with respect to a specific retention
policy.
Table 3 Snapshot retention policy and maximum number of retained snapshots
Maximum number of snapshots retained
Scheduled remote snapshot retention policy
n + 2 of primary snapshots x + 2 of remote snapshots
n of primary snapshots x of remote snapshots
n + 2 primary snapshots older than nx + 2 remote
snapshots older than x
n of hours for primary snapshots x of hours for remote
snapshots
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Understanding and planning Remote Copy