This rambles a bit. Here's the summary: btrfs is currently optimized for normal ... | Hacker News

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		aliguori on July 14, 2011 \| parent \| context \| favorite \| on: Why Virtual Machines suck when you run them from B... This rambles a bit. Here's the summary: btrfs is currently optimized for normal applications that do open("foo", O_RDWR). With this mode, integrity semantics are quite loose in POSIX. Because VMs emulate physical hardware with strong integrity semantics, they usually do either open("foo", O_DIRECT) or open("foo", O_SYNC). btrfs sucks for O_SYNC. It's not just VMs, databases also tend to make heavy use of O_SYNC.

gaius on July 14, 2011 [–]

Ironic that BTRFS is sponsored by Oracle then!

aliguori on July 14, 2011 | [–]

A lot of filesystems don't optimize O_SYNC heavily until it becomes necessary. ext4 has really bad O_SYNC performance until pretty recently FWIW.

Given where BTRFS is right now development wise, it's not at all surprising O_SYNC hasn't been optimized yet.

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