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Optimistic Crash Consistency Vijay Chidambaram Thanumalayan Sankaranarayana Pillai Andrea Arpaci-Dusseau Remzi Arpaci-Dusseau Crash Consistency Problem Single file-system operation updates multiple on-disk data structures System may crash in middle of updates File-system is partially (incorrectly) updated WISDOM Workshop 14 2 Performance OR Consistency Crash-consistency solutions degrade performance Users forced to choose between high performance and strong consistency - Performance differs by 10x for some workloads Many users choose performance - ext3 default configuration did not guarantee crash consistency for many years - Mac OSX does not ensure data is safe fsync() “The Fast drives out the Slow even if the Fast is wrong” - Kahan WISDOM Workshop 14 3 Ordering and Durability Crash consistency is built upon ordered writes File systems conflate ordering and durability - Ideal: {A, B} -> {C} (made durable later) - Current scenario • {A, B} durable • {C} durable Inefficient when only ordering is required WISDOM Workshop 14 4 Can a file system provide both high performance and strong consistency? WISDOM Workshop 14 5 Can a file system provide both high performance and strong consistency? Is there a middle ground between: high performance but no consistency strong consistency but low performance? WISDOM Workshop 14 5 Our solution Optimistic File System (OptFS) WISDOM Workshop 14 6 Our solution Optimistic File System (OptFS) Journaling file system that provides performance and consistency by decoupling ordering and durability WISDOM Workshop 14 6 Our solution Optimistic File System (OptFS) Journaling file system that provides performance and consistency by decoupling ordering and durability Such decoupling allows OptFS to trade freshness for performance while maintaining crash consistency WISDOM Workshop 14 6 Results Techniques: checksums, delayed writes, etc. OptFS provides strong consistency - Equivalent to ext4 data journaling OptFS improves performance significantly - 10x better than ext4 on some workloads New primitive osync() provides ordering among writes at high performance WISDOM Workshop 14 7

Description:
WISDOM Workshop 14. Results. Techniques: checksums, delayed writes, etc. OptFS provides strong consistency. - Equivalent to ext4 data journaling. OptFS improves performance significantly. - 10x better than ext4 on some workloads. New primitive osync() provides ordering among writes at high
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Optimistic Crash Consistency Vijay Chidambaram Thanumalayan Sankaranarayana Pillai Andrea Arpaci-Dusseau Remzi Arpaci-Dusseau Crash Consistency Problem Single file-system operation updates multiple on-disk data structures System may crash in middle of updates File-system is partially (incorrectly) updated WISDOM Workshop 14 2 Performance OR Consistency Crash-consistency solutions degrade performance Users forced to choose between high performance and strong consistency - Performance differs by 10x for some workloads Many users choose performance - ext3 default configuration did not guarantee crash consistency for many years - Mac OSX does not ensure data is safe fsync() “The Fast drives out the Slow even if the Fast is wrong” - Kahan WISDOM Workshop 14 3 Ordering and Durability Crash consistency is built upon ordered writes File systems conflate ordering and durability - Ideal: {A, B} -> {C} (made durable later) - Current scenario • {A, B} durable • {C} durable Inefficient when only ordering is required WISDOM Workshop 14 4 Can a file system provide both high performance and strong consistency? WISDOM Workshop 14 5 Can a file system provide both high performance and strong consistency? Is there a middle ground between: high performance but no consistency strong consistency but low performance? WISDOM Workshop 14 5 Our solution Optimistic File System (OptFS) WISDOM Workshop 14 6 Our solution Optimistic File System (OptFS) Journaling file system that provides performance and consistency by decoupling ordering and durability WISDOM Workshop 14 6 Our solution Optimistic File System (OptFS) Journaling file system that provides performance and consistency by decoupling ordering and durability Such decoupling allows OptFS to trade freshness for performance while maintaining crash consistency WISDOM Workshop 14 6 Results Techniques: checksums, delayed writes, etc. OptFS provides strong consistency - Equivalent to ext4 data journaling OptFS improves performance significantly - 10x better than ext4 on some workloads New primitive osync() provides ordering among writes at high performance WISDOM Workshop 14 7

Description:
WISDOM Workshop 14. Results. Techniques: checksums, delayed writes, etc. OptFS provides strong consistency. - Equivalent to ext4 data journaling. OptFS improves performance significantly. - 10x better than ext4 on some workloads. New primitive osync() provides ordering among writes at high
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