On Mon, Aug 24, 2009 at 11:25:19PM +0200, Pavel Machek wrote: > > I have to admit that I have not paid enough attention to this specifics > > of your ext3 + flash card issue - is it the ftl stuff doing out of order > > IO's? > > The problem is that flash cards destroy whole erase block on unplug, > and ext3 can't cope with that. Sure --- but name **any** filesystem that can deal with the fact that 128k or 256k worth of data might disappear when you pull out the flash card while it is writing a single sector? > > Your statement is overly broad - ext3 on a commercial RAID array that > > does RAID5 or RAID6, etc has no issues that I know of. > > If your commercial RAID array is battery backed, maybe. But I was > talking Linux MD here. It's not just high end RAID arrays that have battery backups; I happen to use a mid-range hardware RAID card that comes with a battery backup. It's just a matter of choosing your hardware carefully. If your concern is that with Linux MD, you could potentially lose an entire stripe in RAID 5 mode, then you should say that explicitly; but again, this isn't a filesystem specific cliam; it's true for all filesystems. I don't know of any file system that can survive having a RAID stripe-shaped-hole blown into the middle of it due to a power failure. I'll note, BTW, that AIX uses a journal to protect against these sorts of problems with software raid; this also means that with AIX, you also don't have to rebuild a RAID 1 device after an unclean shutdown, like you have do with Linux MD. This was on the EVMS's team development list to implement for Linux, but it got canned after LVM won out, lo those many years ago. Ce la vie; but it's a problem which is solvable at the RAID layer, and which is traditionally and historically solved in competent RAID implementations. - Ted -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
