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. Remapped failed sectors would cause this micro-timing to fail, but only for the remapped sectors.
Bob -- Bob Friesenhahn bfrie...@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/ GraphicsMagick Maintainer, http://www.GraphicsMagick.org/ _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
