> From: [email protected] [mailto:discuss- > [email protected]] On Behalf Of Bill Bogstad > > Guessing here.... > > 1. SSDs are constantly moving data around in order to do wear leveling.
Sorry, that's not correct. Wear leveling goes like this: The OS requests to write Block 0. Internally, the drive maintains a map, like NAT. When the OS requests to write block 0, I'll actually write block 743, but I'll remember from now on, that Block 0 on the OS side of the interface, maps to 743 internally. If the OS keeps requesting to overwrite block 0 over and over again, I just keep remapping OS Block 0 goes to 912, now 544, now ... whatever. This way, no individual memory block *actually* gets overwritten and overwritten and overwritten. The actually memory pages have the writes distributed amongst each other, approximately even. > 2. Not all SSDs have batteries/super capacitors to finish those activities if > power is lost. In both SSD's and HDD's, there exists a volatile memory write buffer, which is vulnerable to power loss. When the OS needs to know that some particular data has been flushed to nonvolatile storage, the OS issues a flush command to the drive. The drive then flushes the volatile buffer, and signals the OS that the flush has completed. Same is true for both SSD and HDD. _______________________________________________ Discuss mailing list [email protected] http://lists.blu.org/mailman/listinfo/discuss
