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Tag: OpenStorageSummit

Chris George from DDRdrive put together a great presentation at the OpenStorage summit looking at the ZFS intent log (ZIL), and how their product is particularly well-suited as a ZIL device. Chris did a particularly interesting analysis of the I/O pattern ZFS generates to ZIL devices (using DTrace of course). With writes to a single ZFS dataset, writes are almost 100% sequential, but with activity to multiple datasets, writes become significantly more non-sequential. The ZIL was initially designed to accelerate performance with a dedicated hard drive, but the Hybrid Storage Pool found a significantly better ZIL device in write-optimized, flash SSDs.

In the 7000 series, the performance of these SSDs — called Logzillas — aren’t particularly sensitive to random write patters. Less sophisticated, cheaper SSDs are more significantly impacted by randomness in that both performance and longevity can suffer.

Chris concludes that NV-DRAM is better suited than flash for the ZIL (Oracle’s Logzilla built by STEC actually contains a large amount of NV-DRAM). I completely agree; further, if HDDs and commodity SSDs continue to be target ZIL devices, ZFS could and should do more to ensure that writes are sequential.

I had the chance to speak at the OpenStorage Summit a couple of weeks ago about RAID-Z (the ZFS implementation of RAID). The talk was an accumulation of blog posts and articles written by me and others as well as quite a bit of new material that’s been building up. The talk was an overview of the history of RAID-Z, the strengths and weaknesses that have emerged, and a look towards the challenges ahead for ZFS and RAID with some possible solutions and mitigating factors. Thanks to Nexenta for putting the conference together; questions or comments are very welcome.

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