Recently, I've been reading through the ZIL/slog discussion and have the impression that a lot of folks here are (like me) interested in getting a viable solution for a cheap, fast and reliable ZIL device. I think I can provide such a solution for about $200, but it involves a lot of development work. The basic idea: the main problem when using a HDD as a ZIL device are the cache flushes in combination with the linear write pattern of the ZIL. This leads to a whole rotation of the platter after each write, because after the first write returns, the head is already past the sector that will be written next. My idea goes as follows: don't write linearly. Track the rotation and write to the position the head will hit next. This might be done by a re-mapping layer or integrated into ZFS. This works only because ZIL device are basically write-only. Reads from this device will be horribly slow.
I have done some testing and am quite enthusiastic. If I take a decent SAS disk (like the Hitachi Ultrastar C10K300), I can raise the synchronous write performance from 166 writes/s to about 2000 writes/s (!). 2000 IOPS is more than sufficient for our production environment. Currently I'm implementing a re-mapping driver for this. The reason I'm writing to this list is that I'd like to find support from the zfs team, find sparring partners to discuss implementation details and algorithms and, most important, find testers! If there is interest it would be great to build an official project around it. I'd be willing to contribute most of the code, but any help will be more than welcome. So, anyone interested? :) -- Arne Jansen _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
