On Mon, April 12, 2010 12:28, Tomas Ögren wrote: > On 12 April, 2010 - David Magda sent me these 0,7K bytes: > >> On Mon, April 12, 2010 10:48, Tomas Ögren wrote: >> >> > For flash to overwrite a block, it needs to clear it first.. so yes, >> > clearing it out in the background (after erasing) instead of just >> > before the timing critical write(), you can make stuff go faster. >> >> Except that ZFS does not overwrite blocks because it is copy-on-write. > > So CoW will enable infinite storage, so you never have to write on the > same place again? Cool.
Your comment was regarding making write()s go faster by pre-clearing unused blocks so there's always writable blocks available. Because ZFS doesn't go to the same LBAs when writing data, the SSD doesn't have to worry about read-modify-write circumstances like it has to with traditional file systems. Given that ZFS probably would not have to go back to "old" blocks until it's reached the end of the disk, that should give the SSDs' firmware plenty of time to do block-remapping and background erasing--something that's done now anyway regardless of whether an SSD supports TRIM or not. You don't need TRIM to make ZFS go fast, though it doesn't hurt. There will be no "timing critical" instances as long as there is a decent amount of free space available and ZFS can simply keep doing an LBA++. SSDs worked fine without TRIM, it's just that command helps them work more efficiently. _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
