Lustre 1.8

Lustre 1.8 introduces several robust, new features and improved system functionality. This page provides descriptions of these features and lists the benefits offered by upgrading to Lustre 1.8.

Adaptive Timeouts
The adaptive timeouts feature (enabled, by default, in release 1.8) causes Lustre to use an adaptive mechanism to set RPC timeouts. RPC service time histories are tracked on all servers, and estimates for future RPCs are reported back to clients. Clients use these service time estimates along with their own observations of the network delays to set future RPC timeout values.

If server request processing slows down, its estimates increase and the clients allow more time for RPC completion before retrying. If RPCs queued up on the server approach their timeouts, the server sends early replies to the client, telling it to allow more time. Conversely, as the load on the server is reduced, the RPC timeout values decrease, allowing faster client detection of non-responsive servers and faster attempts to reconnect to a server's failover partner.

Why should I upgrade to Lustre 1.8 to get it?
Adaptive timeouts offers these benefits:


 * Relieves users from having to tune the obd_timeout value.
 * Reduces RPC timeouts and disconnect/reconnect cycles.

Additional Resources
For more information about adaptive timeouts, see:


 * Architecture Page - Adaptive timeouts (use cases)
 * HLD - Adaptive RPC timeouts

Client Interoperability
The client interoperability feature enables Lustre 1.8 clients to work with the new network protocol that will be introduced in the 2.0 release. This functionality allows transparent client, server, network and storage interoperability during migration from 1.6-based clusters to clusters with 2.0-based servers.

Client interoperability provides the following support:


 * Lustre 1.8 client can communicate with 1.8 components, including servers and other clients.
 * Lustre 1.8 client can communicate with 1.6 components, including servers and other clients.
 * Lustre 1.8 client can communicate with 2.0 servers.

Why should I upgrade to Lustre 1.8 to get it?
Client interoperability offers this benefit:


 * When Lustre 2.0 is released, perform a 'live' upgrade from 1.8 to 2.0 without needing to shut down the system.

Additional Resources
For more information on client interoperability, see:


 * Architecture page - Interoperability FIDs and ZFS
 * HLD - Interoperability at the Server Side
 * HLD - Sptlrpc interoperability
 * DLD - Interoperable Client Recovery
 * DLD - Sptlrpc interoperability

OSS Read Cache
The OSS read cache feature provides read-only caching of data on an OSS. It uses a regular Linux pagecache to store the data. OSS read cache improves Lustre performance when several clients access the same data set, and the data fits the OSS cache (which can occupy most of the available memory). The overhead of OSS read cache is very low on modern CPUs, and cache misses do not negatively impact performance compared to Lustre releases before OSS read cache was available.

Why should I upgrade to Lustre 1.8 to get it?
OSS read cache can improve Lustre performance, and offers these benefits:


 * Allows OSTs to cache read data more frequently
 * Improves repeated reads to match network speeds instead of disk speeds
 * Provides the building block for OST write cache (small write aggregation)

Additional Resources
For more information on OSS read cache, see:


 * Architecture page - Caching OSS

OST Pools
The OST pools feature allows the administrator to name a group of OSTs for file striping purposes. For instance, a group of local OSTs could be defined for faster access; a group of higher-performance OSTs could be defined for specific applications; a group of non-RAID OSTs could be defined for scratch files; or groups of OSTs could be defined for particular users.

Pools are defined by the system administrator, using regular Lustre tools (lctl). Pool usage is specified and stored along with other striping information (e.g., stripe count, stripe size) for directories or individual files (lfs setstripe or llapi_create_file). Traditional automated OST selection optimizations (QOS) occur within a pool (e.g., free-space leveling within the pool). OSTs can be added or removed from a pool at any time (and existing files always remain in place and available.)

OST pools characteristics include:


 * An OST can be associated with multiple pools
 * No ordering of OSTs is implied or defined within a pool
 * OST membership in a pool can change over time
 * a directory can default to a specific pool and new files/subdirectories created therein will use that pool

NOTE: In its current implementation, the OST pools feature does not implement an automated policy or restrict users from creating files in any of the pools; it must be managed directly by administrator/user. It is a building block for policy-managed storage.

Why should I upgrade to Lustre 1.8 to get it?
OST pools offers these benefits:


 * Allows sets of OSTs to be managed via named groups
 * Pools can separate heterogeneous OSTs within the same filesystem
 * Fast vs. slow disks
 * Local network vs. remote network (e.g. WAN)
 * RAID 1 vs. RAID5 backing storage, etc.
 * Specific OSTs for users/groups/applications (by directory)
 * Easier disk usage policy implementation for administrators
 * Hardware can be more closely optimized for particular usage patterns
 * Human-readable stripe mappings

Additional Resources
For more information on OST pools, see:


 * Architecture page - OST pools
 * DLD - OST Pools
 * Test plan - OST pools

Version-Based Recovery
Version-based Recovery (VBR) improves the robustness of client recovery operations and allows Lustre to recover, even if multiple clients fail at the same time as the server. With VBR, recovery is more flexible; not all clients are evicted if some miss recovery, and a missed client may try to recover after the server recovery window.

Why should I upgrade to Lustre 1.8 to get it?
VBR functionality in Lustre 1.8 allows more flexible recovery after a failure. In previous Lustre releases recovery would stop if any client was missing, even if the failed clients were not modifying the filesystem or if they were working in an unrelated part of the filesystem, and the remaining clients would be evicted. With VBR, the recovery will continue even if some clients are missed, and the missed clients can try to recover later. With VBR, Lustre clients may successfully recover in a wider variety of failure scenarios.

VBR offers these benefits:


 * Improves the robustness of client recovery operations
 * Allows Lustre recovery to work even if multiple clients fail at the same time as the server, if the remaining clients are working independently
 * Provides a building block for disconnected client operations

Additional Resources
For more information on VBR, see:


 * Architecture page - VBR
 * HLD - VBR
 * DLD - VBR
 * Test plan - VBR