Data Manager¶

The Data Manager enforces policies and generates reports about storage resource usage. The Data Manager interacts with the Keep server and the metadata database. Clients/users do not interact with the Data Manager directly.

See also:

• Keep server
• Keep manifest format
• source: n/a (design phase)

Responsibilities:

• Garbage collector: decide what is eligible for deletion (and some partial order of preference)
• Replication enforcer: copy and delete blobs in various backing stores to achieve desired replication level
• Rebalancer: move blobs to redistribute free space and reduce client probes
• Tell managers how much disk space is being conserved due to CAS
• Tell managers how much disk space is occupied in a given backing store service
• Tell managers how disk usage would be affected by modifying storage policy
• Tell managers how much disk space+time is used (per user, group, node, disk)
• Tell users when replication/policy specified for a collection is not currently satisfied (and why, for how long, etc)
• Tell users how much disk space is represented by a given set of collections
• Tell users how much disk space can be made available by garbage collection
• Tell users how soon they should expect their cached data to disappear
• Tell users performance statistics (how fast should I expect my job to read data?)
• Tell ops where each block was most recently read/written, in case data recovery is needed
• Tell ops how unbalanced the backing stores are across the cluster
• Tell ops activity level and performance statistics
• Tell ops activity level vs. amount of space (how much of the data is being accessed by users?)
• Tell ops disk performance/error/status trends (and SMART reports) to help identify bad hardware
• Tell ops history of disk adds, removals, moves

Basic kinds of data in the index:

• Which blocks are used by which collections (and which collections are valued by which users/groups)
• Which blocks are stored on which disks
• Which disks are attached to which nodes
• Read events
• Write events
• Exceptions (checksum mismatch, IO error)

Implementation considerations¶

Overview

• REST service
• API server may cache/proxy some queries
• API server may redirect some queries

Permissions

• Support +A tokens like Keep server when accepting collection/blob uuids in request?
• Require admin api_token for some queries, site-configurable?

Distributed/asynchronous

• Easy to run multiple keep index services.
• Most features do not need synchronous operation / real time data.
• Features that move or delete data should be tied to a single "primary" indexing service (failover event likely requires resetting some state).
• Substantial disagreement between multiple index services should be easy to flag on admin dashboard.