Bob Friesenhahn wrote: > On Wed, 26 May 2010, sensille wrote: >> 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 like your idea. It would require a profiling application to learn the > physical geometry and timing of a given disk drive in order to save the > configuration data for it. The timing could vary under heavy system > load so the data needs to be sent early enough that it will always be > there when needed. The profiling application might need to drive a disk > for several hours (or a day) in order to fully understand how it > behaves.
A day is a good landmark. Currently the application runs several hours just to map the tracks. But there's lots of room for algorithms that measure and fine-tune on the fly. Every write is also a measurement. > Remapped failed sectors would cause this micro-timing to fail, > but only for the remapped sectors. Of course you could detect those remapped sectors because of the failed timing and stop using them in the future :) -- Arne > Bob _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
