On Wed, 10 Sep 2008, Keith Bierman wrote: >> written at once, 512KB needs to be erased at once. This means that >> write performance to an empty device will seem initially pretty good, >> but then it will start to suffer as 512KB regions need to be erased to >> make space for more writes. > > That assumes that one doesn't code up the system to batch up erases prior to > writes.
Is the notion of block "erase" even exposed via SATA/SCSI protocols? Maybe it is for CD/DVD type devices. This is something that only the device itself would be aware of. Only the device knows if the block has been used before. Only the device knows the block of physical storage which will be used for the write. The device does not know what can be erased before it sees a (over) write request and if the write request is for a smaller size, then existing data needs to be moved (for leveling) or buffered and written back to the same locations. This means that 512KB needs to be erased and re-written. > Presumably anyone deft enough to design such an enterprise grade device will > be able to provide enough super-capacitor (or equivalent) to ensure that DRAM > is flushed to SSD before anything bad happens. That is reasonable. It adds to product cost and size though. Super-capacitors are not super-small. Bob ====================================== Bob Friesenhahn [EMAIL PROTECTED], 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
