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We use ZFS for root, but not content. For content we use UFS. This is because ZFS is not compatible with "zero-copy" sendfile, since it uses its own ARC cache rather than the kernel page cache, meaning sending data stored on ZFS requires an extra data copy out of the ARC. Its also not compatible with async sendfile, as it does not have the methods required to call the sendfile completion handler after data is read from disk into memory.

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>For content we use UFS

I found this extremely interesting. ZFS is almost a cure-all for what ails you WRT storage, but there is always something that even Superman can't do. Sometimes old-school is best-school.

Thanks for the presentation and QA!

Would netflix benefit if zfs was modified to use a unified cache to make zero-copy possible?

Possibly. Remember the goal is to keep data read from the drives unmapped in the kernel address space, and hence never accessed by the CPU for efficiency. So we'd have to give up, or at least alter, zfs to not do checksums each time a block is read.

The most interesting use of ZFS for us would be on servers with traditional hard drives, where ZFS is supposedly more efficient than UFS at keeping data contiguous on disk, thus resulting in fewer seeks and increased read bandwidth.

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