"I wasn't planning on releasing v0.12 yet, and it was supposed to have some initial support for multiple devices. But, I have made a number of performance fixes and small bug fixes, and I wanted to get them out there before the (destabilizing) work on multiple-devices took over," explained Chris Mason [1] regarding the 0.12 release of his new btrfs filesytem. Btrfs was first announced in June of 2007, as an alpha-quality filesystem offering checksumming of all files and metadata, extent based file storage, efficient packing of small files, dynamic inode allocation, writable snapshots, object level mirroring and striping, and fast offline filesystem checks, among other features. The project's website [2] explains, "Linux has a wealth of filesystems to choose from, but we are facing a number of challenges with scaling to the large storage subsystems that are becoming common in today's data centers. Filesystems need to scale in their ability to address and manage large storage, and also in their ability to detect, repair and tolerate errors in the data stored on disk." Regarding the latest release, Chris offered:
"So, here's v0.12. It comes with a shiny new disk format (sorry), but the gain is dramatically better random writes to existing files. In testing here, the random write phase of tiobench went from 1MB/s to 30MB/s. The fix was to change the way back references for file extents were hashed."
From: Chris Mason <chris.mason@...>
Subject: [ANNOUNCE] Btrfs v0.12 released
[2]Date: Feb 6, 1:00 pm 2008
Hello everyone,
I wasn't planning on releasing v0.12 yet, and it was supposed to have some
initial support for multiple devices. But, I have made a number of
performance fixes and small bug fixes, and I wanted to get them out there
before the (destabilizing) work on multiple-devices took over.
So, here's v0.12. It comes with a shiny new disk format (sorry), but the gain
is dramatically better random writes to existing files. In testing here, the
random write phase of tiobench went from 1MB/s to 30MB/s. The fix was to
change the way back references for file extents were hashed.
Other changes:
Insert and delete multiple items at once in the btree where possible. Back
references added more tree balances, and it showed up in a few benchmarks.
With v0.12, backrefs have no real impact on performance.
Optimize bio end_io routines. Btrfs was spending way too much CPU time in the
bio end_io routines, leading to lock contention and other problems.
Optimize read ahead during transaction commit. The old code was trying to
read far too much at once, which made the end_io problems really stand out.
mount -o ssd option, which clusters file data writes together regardless of
the directory the files belong to. There are a number of other performance
tweaks for SSD, aimed at clustering metadata and data writes to better take
advantage of the hardware.
mount -o max_inline=size option, to override the default max inline file data
size (default is 8k). Any value up to the leaf size is allowed (default
16k).
Simple -ENOSPC handling. Emphasis on simple, but it prevents accidentally
filling the disk most of the time. With enough threads/procs banging on
things, you can still easily crash the box.
-chris
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