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Btrfs: From Enterprise to Mobile World

Agenda. Btrfs FeaturesBtrfs BasicsBtrfs UtilityBtrfs on mobile devicesChallenges from meego perspectiveBtrfs Community. Features. Extent based file storageCopy on write metadata and dataSpace efficient packing of small files Subvolume/snapshotSoftware RAIDChecksums on data and metadataOpt

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Btrfs: From Enterprise to Mobile World

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    1. Btrfs: From Enterprise to Mobile World Xin Zhong, Chengwei Yang Intel OTC China

    2. Agenda Btrfs Features Btrfs Basics Btrfs Utility Btrfs on mobile devices Challenges from meego perspective Btrfs Community

    3. Features Extent based file storage Copy on write metadata and data Space efficient packing of small files Subvolume/snapshot Software RAID Checksums on data and metadata Optional transparent compression Online resize, defragmentation, device management Integrated multiple device support

    4. Btrfs Basics Btrfs = btree fs Btree is the core data structure for all metadata Copy-On-Write Ideal for clone/snapshot Allocate at alternative localtion. Easy for allocation clustering.Allocate at alternative localtion. Easy for allocation clustering.

    5. Btrfs Utility: btrfs-progs Mkfs.btrfs Btrfs Subvolume, device, filesystem Btrfs-debug-tree Btrfsck (under development)

    6. Btrfs on mobile devices Data integrity Backup/restore Compression SSD optimization Performance

    7. Data integrity Single device support Crc32 checksum on data and metadata Separate checksum tree Checksum failure handling Data checksum can be turned off by –o nodatasum mount option

    8. Backup/Restore Space efficient due to COW Useful for OS upgrade/revert Steps Create subvolume Set default mount point Create snapshot Reset default mount point

    9. Compression Two algorithms are supported in 2.6.38 Gzip Lzo Tradeoff between compression ratio and speed Enabled by –o compress=gzip|lzo mount option Default is gzip (-o compress)

    10. Compression – space usage

    11. Compression - performance

    12. SSD Optimization SSD characteristic Page for read & write (4KB) Block for erase (64 pages) Erase before re-write Btrfs for SSD Auto detection for non-rotating device Force it by –o ssd mount option Allocation clustered in 2M chunk In SSD mode, last allocation place inside an allocation chunk will be remembered for data. And 2M chunk will be allocated for metadata. It make write sequentially since it can not find big enough chunk backward. But it will spread out metadata and make fsck slower. So it’s not default for non-SSD device. This will cause free space fragmenation. But the problem can be reduce by merge fragment into one cluster.In SSD mode, last allocation place inside an allocation chunk will be remembered for data. And 2M chunk will be allocated for metadata. It make write sequentially since it can not find big enough chunk backward. But it will spread out metadata and make fsck slower. So it’s not default for non-SSD device. This will cause free space fragmenation. But the problem can be reduce by merge fragment into one cluster.

    13. SSD Performance Explain verticle axis first. More numbers are available. No enough time to prepare for all of them.Explain verticle axis first. More numbers are available. No enough time to prepare for all of them.

    14. Chanllenges from meego perspective

    15. Community Development Testing Cooperation Our contributions are well recognized Patches are integrated very fast Special case are considered Explore more features…

    16. Reference Btrfs wiki http://btrfs.wiki.kernel.org/index.php/Main_Page Btrfs history https://lwn.net/Articles/342892/ PTS http://www.phoronix.com/ http://phoronix-test-suite.com

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