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The following tables provide definitions for some of the terms that are used in this document.
Term |
Definition |
Source volume |
A LUN or mainframe CKD volume that is protected by snapshots or clones. |
Snapshot |
A preserved, point-in-time image of a source volume. |
Targetless snapshot |
A snapshot used by SnapVX that does not require a target LUN or CKD volume. |
Source snap |
An optional setting for SnapVX targetless snapshots that prevents a user from deleting snapshots accidentally or intentionally. Secure snapshots may only be terminated after they expire or by customer-authorized Dell Support. See the Dell Support knowledge base article 498316 for more information. |
Snapshot delta |
A point-in-time version of a source volume track that was preserved during a host write to a source volume that had an active snapshot. |
Replication cache |
A portion of the metadata in cache that is dedicated for replication data pointers (RDP) which track the snapshot deltas in the SRP. Replication cache usage increases as SnapVX and VP snap source devices are written to, as there is more point-in-time data to manage. |
Linked target volume |
A LUN that is linked to a SnapVX snapshot to make the point-in-time of the snapshot accessible to a host. |
zDP |
Data Protector for Z Systems (zDP) is a Dell EMC z/OS-based application that uses TimeFinder SnapVX snapshots to enable rapid recovery from logical data corruption on IBM z Systems. zDP achieves this functionality by providing multiple, frequent, and consistent point-in-time copies of data in an automated fashion across multiple volumes from which an application-level recovery can be conducted. For more information about zDP, see the document Dell EMC PowerMax and VMAX All Flash: Data Protector for z Systems (zDP) Essentials. |
Coordinated Universal Time (UTC) |
The primary time standard by which the world regulates clocks and time. It is not adjusted for daylight saving time. |
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Term |
Definition |
Effective policies |
Snapshot policies that are operating (not suspended) on a storage group (SG) on the PowerMax or VMAX All Flash (AF) array. |
Inherited |
Term that describes how a snapshot policy that applied to a parent SG is inherited by all child SGs. |
Recovery point objective (RPO) |
Unisphere for PowerMax definitions for the frequency at which a Snapshot Policy takes snapshots, and when the snapshots should be taken. Solutions Enabler refers to these settings as the Interval and the Offset, respectively.
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Max mount |
The maximum number of snapshots that should be maintained for a specified Snapshot Policy. The maximum count must be between 1 and 1024. |
Warning compliance |
User-defined snapshot count at which warning alerts are posted. The user sets the attribute on each Snapshot Policy. The compliance count cannot be set to 0 and must be less than or equal to the maximum count of the Snapshot Policy. If the critical compliance count is also set, the warning compliance count must be greater than or equal to that. |
Critical compliance |
User-defined snapshot count at which critical alerts are posted. The user sets the attribute on each Snapshot Policy. The compliance count cannot be set to 0 and must be less than or equal to the maximum count of the Snapshot Policy. If the warning compliance count is also set, the critical compliance count must be less than or equal to that count. |
Persistent policy snapshots |
Setting a policy snapshot to persistent excludes it from being automatically recycled by the policy parameters. A persistent snapshot is not automatically terminated until the user clears the persistent setting and the policy retention time has passed, or if the snapshot is manually terminated by the user. |
Orphaned |
When a policy is deleted, snapshots that the policy created are renamed to _Orphaned. The expiration date is set earlier when the SG was removed from the policy. Orphaned snapshots can be used for link and restore operations and can be manually terminated. |
Cloud snapshots |
Cloud Mobility for Dell EMC PowerMax provides open-systems snapshot movement to and from private and public clouds (Dell EMC ECS, AWS, Microsoft Azure) for recovering data back to the array and consumed it directly in AWS. |
Out-of-window exception |
Indication that a SnapSet has a policy snapshot with a timestamp that is outside of the policy window. Possible reasons include modification of a policy or snapshots prevented from being terminated as scheduled due to being set as persistent, being in a restore state, or linked to a target. |
Gap exception |
Indication that a SnapSet has policy snapshots that were taken at intervals that are larger than defined in the policy. Possible reasons include failure to create a regularly scheduled snapshot, termination of a snapshot, or modification of a policy. |
The following SnapVX terms are introduced in the PowerMaxOS Q3 2020 release. These terms are applicable to all snapshots and are not unique to snapshot policies.
Term |
Definition |
SnapSet |
A set of consistent snapshots that are taken together. For example, when a snapshot is taken of an SG that contains 10 devices, the resulting SnapSet consists of 10 consistent snapshots. |
SnapSet ID |
A system-generated number that is applied to consistent snapshots across the volumes in a SnapSet. When a snapshot is taken of an SG, all resulting snapshots have the same SnapSet ID. The SnapSet ID is an absolute value that does not adjust as other snapshots are created or terminated. |
Bulk terminate |
A Unisphere term for functionality that allows termination of many snapshots of an SG in a single operation. |