Adam Leventhal's blog

Search
Close this search box.

ZIL analysis from Chris George

November 15, 2010

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.

Recent Posts

January 13, 2024
December 29, 2023
February 12, 2017
December 18, 2016
August 9, 2016

Archives

Archives