On Wed, February 11, 2009 11:21, Bob Friesenhahn wrote: > On Wed, 11 Feb 2009, Tim wrote: >> >> All that and yet the fact remains: I've never "ejected" a USB drive from >> OS >> X or Windows, I simply pull it and go, and I've never once lost data, or >> had >> it become unrecoverable or even corrupted. >> >> And yes, I do keep checksums of all the data sitting on them and >> periodically check it. So, for all of your ranting and raving, the fact >> remains even a *crappy* filesystem like fat32 manages to handle a hot >> unplug >> without any prior notice without going belly up. > > This seems like another one of your trolls. Any one of us who have > used USB drives under OS-X or Windows knows that the OS complains > quite a lot if you just unplug the drive so we all learn how to do > things properly.
Then again, I've never lost data during the learning period, nor on the rare occasions where I just get it wrong. This is good; not quite remembering to eject a USB memory stick is *so* easy. We do all know why violating protocols here works so much of the time, right? It's because Windows is using very simple, old-fashioned strategies to write to the USB devices. Write caching is nonexistent, or of very short duration, for example. So if IO has quiesced to the device, it's been several seconds since the last IO, it's nearly certain to just pull it. Nearly. ZFS is applying much more modern, much more aggressive, optimizing strategies. This is entirely good; ZFS is intended for a space where that's important a lot of the time. But one tradeoff is that those rules become more important. > You must have very special data if you compute independent checksums > for each one of your files, and it leaves me wondering why you think > that data is correct due to being checksummed. Checksumming incorrect > data does not make that data correct. Can't speak for him, but I have par2 checksums and redundant data for lots of my old photos on disk. I created them before writing archival optical disks of the data, to give me some additional hope of recovering the data in the long run. I don't, in fact, know that most of those photos are actually valid data; only the ones I've viewed after creating the par2 checksums (and I can't rule out weird errors that don't result in corrupting the whole rest of the image even then). Still, once I've got the checksum on file, I can at least determine that I've had a disk error in many cases (not quite identical to determining that the data is still valid; after all, the data and the checksum could have been corrupted in such a way that I get a false positive on the checksum). -- David Dyer-Bennet, d...@dd-b.net; http://dd-b.net/ Snapshots: http://dd-b.net/dd-b/SnapshotAlbum/data/ Photos: http://dd-b.net/photography/gallery/ Dragaera: http://dragaera.info _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
