2. © 2012 Whamcloud, Inc. Distributed Namespace Status Phase I - Remote Directories Wang Di Whamcloud, Inc.

3. © 2012 Whamcloud, Inc. Subdirectories on a remote metadata target Scales MDT namespace, like OSTs can today Dedicated performance for users/jobs All MDTs can use any/all OSTs to create objects DNE Phase I - Remote Directory MDT1 rose dir1 file MDT0 root file bill MDT2 frank file dir2 Lustre User Group 2012 3

4. © 2012 Whamcloud, Inc. Remote directory creation by administrator only –Remote directory creation is a synchronous disk operation lfs mkdir -i {mdtidx} /path/to/remote_dir Files/subdirs created in remote dir stay on MDT –Local operations (create, unlink, open, close) at maximum performance –Limit RPCs that need to communicate with multiple MDTs –Simplifies implementation for initial deployment Remote Directory Implementation 4 Lustre User Group 2012

5. © 2012 Whamcloud, Inc. Failed/disabled MDT affects all of its subtrees –Accessing failed/disabled MDT will return EIO –Disabling MDT0 causes whole namespace to be inaccessible Remote directory can only be created on MDT0 –Otherwise, failure of one MDT would isolate other MDTs Rename or link across MDTs returns –EXDEV Deliberate limitation of complexity –Limit testing, recovery, failure scenarios for initial deployment –Restrictions relaxed as experience is gained, or via override Remote Directory Limitations 5 Lustre User Group 2012

6. © 2012 Whamcloud, Inc. MDT disk format must use ldiskfs dir_data feature –Default for any 2.x formatted filesystem –Allows storing remote directory entry pointers –Enable on 1.x filesystems: tune2fs -O dir_data /dev/mdt0 Upgrade clients, MGS, MDS, OSS to Lustre 2.4+ –Not required to enable DNE when upgrading to Lustre 2.4+ –Once DNE is enabled, downgrade to older Lustre difficult requires copying/deleting all files not on MDT0 Add new MDTs to running filesystem –Clients without DNE support evicted at this point –New MDTs only used once a remote directory entry is created mkfs.lustre --reformat --mgsnode={mgsnode} --mdt --index=N /dev/{mdtN} mount –t lustre /dev/{mdtN} /mnt/{mdtN} Enable DNE on new/existing filesystem 6 Lustre User Group 2012

7. © 2012 Whamcloud, Inc. Hash a single directory across multiple MDTs Multiple servers active for directory/inodes Improve performance for large directories MDT0MDT3 MDT2 DNE Phase II - Shard/Stripe Directory MDT1 dir.0 dir.2 car cat dir.1 bobdog dir.3 dalebeealeace master slave Lustre User Group 2012 7

8. © 2012 Whamcloud, Inc. Unique cluster-wide identifier for file/directory –Introduced in Lustre 2.0 –Three components form object address {f_seq, f_oid, f_ver} –Large sequence range is allocated to each server –Sequences are large, so FIDs are never re-used FID Location Database (FLDB) maps FID->server –FLDB is known to all clients and servers –Kept small due to few sequence ranges –Sequence is looked up in FLDB to find MDT/OST index Object Index (OI) maps FID->inode on server –OI maps FID to local inode number Lustre File IDentifier (FID) 8 Lustre User Group 2012 VersionSequence #Object # 64 bits 32 bits

9. © 2012 Whamcloud, Inc. Client does filename lookup in parent directory –Root directory lives on MDT0 Client maps FID to Master MDT via FLDB –If request only involves one MDT, same as current single MDT Some operations need to access Slave MDTs –Called cross-MDT operations –Master MDT forwards update(s) other MDT(s) to finish the request –Create/unlink remote directory are only cross-MDT operations today DNE Master and Slave MDTs 9 client FLDB Get Master MDT for this operation Master MDT Slave MDT2 request reply Lustre User Group 2012

10. © 2012 Whamcloud, Inc. Create Remote Directory DNE Operation 10 Lustre User Group 2012

11. © 2012 Whamcloud, Inc. Master MDT checks RPC XID against last_rcvd file –Determines whether the operation was committed to disk or not –Committed: Master MDT reconstructs RPC reply from last_rcvd entry –Uncommitted: Master MDT redoes creation Resend same directory creation RPC to Slave MDT using same FID Slave MDT checks if remote directory was created –Looks up FID requested by Master in local OI –Creates new subdirectory with FID if missing –Returns success to Master Create Resend between MDTs 11 Lustre User Group 2012

12. © 2012 Whamcloud, Inc. Unlink Remote Directory DNE Operation 12 Lustre User Group 2012

13. © 2012 Whamcloud, Inc. Master MDT checks RPC XID against last_rcvd file –Determines whether the operation was committed to disk or not –Committed: Master MDT reconstructs RPC reply from last_rcvd entry –Uncommitted: Master unlinks, deletes name, adds destroy log, etc. If Slave MDT fails during this process –llog sync thread on Master MDT will resend destroy to Slave MDT –Directory unlinks are idempotent, can be retried Unlink Resend between MDTs 13 Lustre User Group 2012

14. © 2012 Whamcloud, Inc. FID is packed into the name entry Each remote entry will have a local agent inode Real object (inode) on Remote MDT found via OI Remote Directory Entry 14 Lustre User Group 2012

15. © 2012 Whamcloud, Inc. Two directories (AGENT and REMOTE) added AGENT –Each remote entry has a local agent inode –Agent inodes located under /AGENT/MDTn, one for each remote MDT REMOTE –Remote directories on Slave MDT created under /REMOTE Keeps local disk filesystem consistent Allows efficient checking of cross links by LFSCK MDT Disk Layout 15 Lustre User Group 2012

16. © 2012 Whamcloud, Inc. Active-Active MDT failover available with DNE –Allows multiple MDTs to be exported from one MDS –Ensures file system remains available in face of MDS node failure –Prevents isolation of large parts of the filesystem DNE High Availability 16 Lustre User Group 2012 MDS1 MDT1MDT2 MDS2 Take over

17. © 2012 Whamcloud, Inc. Internal Architecture 17 Lustre User Group 2012

18. © 2012 Whamcloud, Inc. Testing done on LLNL Hyperion –100 clients, 8 mount points –Separate directory per mount point –One stripe per file Early Test Results 18 Lustre User Group 2012

19. © 2012 Whamcloud, Inc. Wang Di Whamcloud, Inc. Thank You