COW for Flash?

Posted Jun 19, 2007 8:17 UTC (Tue) by joern (guest, #22392)
In reply to: COW for Flash? by qu1j0t3
Parent article: Linus on GPLv3 and ZFS

> It has been said that COW is ideal for Flash. Can you explain why ZFS isn't relevant here?

Raw flash behaves sufficiently different to hard disks that some ZFS design assumptions become untrue. Flash has large erase blocks. Within erase blocks, data must be written from front to back. Writing the block again requires erasing all of it. So the filesystem block size either has to be equal to the erase block size, or you need garbage collection. And with garbage collection comes a nasty deadlock problem most people don't even realize exists. :)

Next comes wear out and protection against it. Afaics, ZFS has several hot zones that receive significantly more writes than others.

I guess those two are the big reasons.