[edit] WARNING: This is the _old_ Lustre wiki, and it is in the process of being retired. The information found here is all likely to be out of date. Please search the new wiki for more up to date information.

Architecture - FIDs on OST

From Obsolete Lustre Wiki
Jump to: navigation, search

Note: The content on this page reflects the state of design of a Lustre feature at a particular point in time and may contain outdated information.

Contents

Summary

We introduce new fids on OST. Using FIDs to identify objects on OSTs needs to be compatible with the existing object IDs used in current Lustre releases. There are two areas that need to maintain compatibility - the numbering of the objects themselves, and their encoding into RPCs in order to communicate between clients and servers.

In order to avoid FID numbers conflicting with existing objects the old objects are mapped into the reserved IDIF namespace as discussed in Interoperability fids zfs, using the ost_idx as part of the IDIF sequence number to disambiguate otherwise identical object numbers on different OSTs.

For network protocol interoperability with existing OSTs and clients the FID numbers must be mapped onto the o_id and o_gr fields.

Definitions

fid
cluster-wide unique identificator
sequence
contiguous set of fids, all fids from given sequence belong to single specific node
fld
persistent sequence to node mapping
object
OST object used to store user's data (what about internal to OST objects, like last_rcvd?)

Requirements

  1. any node can generate fids to be used for OST objects
  2. no orphans after partial recovery
  3. objects to be created on demand (CROW)
  4. backward compatibility?

Use Cases

ID Quality Attribute Summary
new sequence usability, performance client gets sequence from specific OST
create file usability create file on MDS with specified objects
space balance usability,performance how to distribute objects among OSTs
file exists usability create file request finds existing file
reconnect availability reconnect after OST failover
2.0 usability compatibility mode: MDS talks to OST to get new fids
2.x usability clients talk to OST to get new fids
orphan availability server should be able to identify orphan objects

Quality Attribute Scenarios

QAS template

Scenario:
Business Goals:
Relevant QA's:
details Stimulus source:
Stimulus:
Environment:
Artifact:
Response:
Response measure:
Questions:
Personal tools
Navigation