On Sun, Mar 18, 2007 at 03:31:50PM -0500, Josh Boyer wrote: > On Sun, Mar 18, 2007 at 02:18:12PM -0500, Matt Mackall wrote: > > > > I'm well aware of all that. I wrote a NAND driver just last month. > > Let's consider this table: > > > > HARD drives MTD device > > Consists of sectors Consists of eraseblocks > > Sectors are small (512, 1024 bytes) Eraseblocks are larger (32KiB, 128KiB) > > read sector and write sector read, write, and erase block > > Bad sectors are re-mapped Bad eraseblocks are not hidden > > HDD sectors don't wear out Eraseblocks get worn-out > N/A NAND flash addressed in pages > N/A NAND flash has OOB areas > N/A (?) NAND flash requires ECC
Disks have OOB areas with ECC, it's just nicely hidden inside the drive. They also typically have physical sectors bigger than 512 bytes, again hidden. > > If the end goal is to end up with something that looks like a block > > device (which seems to be implied by adding transparent wear leveling > > Nope, not the end goal. It's more about wear-leveling across the entire > flash chip than it is presenting a "block like" device. It seems to be about spanning devices and repartitioning as well. Hence the analogy with LVM. > > and bad block remapping), then I don't see any reason it can't be done > > in device mapper. The 'smarts' of mtdblock could in fact be pulled up > > There is nothing smart about mtdblock. And mtdblock has nothing to do > with UBI. Note the scare quotes. Device mapper runs on top of a block device. And mtdblock is currently the block interface that MTD exports. And it has 'smarts' that hide handling of sub-eraseblock I/O. I'm clearly talking about an approach that doesn't involve UBI at all. > > In the end, a block device is something which does random access > > block-oriented I/O. Disk and NAND both fit that description. > > NAND very much doesn't fit the "random access" part of that. For writes > you have to write in incrementing pages within eraseblocks. And? You can't do I/O smaller than a sector on a disk. -- Mathematics is the supreme nostalgia of our time. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
