On February 13, 2009 12:20:21 PM -0500 Miles Nordin <car...@ivy.net> wrote:
"fc" == Frank Cusack <fcus...@fcusack.com> writes:>> Dropping a flush-cache command is just as bad as dropping a >> write. fc> Not that it matters, but it seems obvious that this is wrong fc> or anyway an exaggeration. Dropping a flush-cache just means fc> that you have to wait until the device is quiesced before the fc> data is consistent. fc> Dropping a write is much much worse. backwards i think. Dropping a flush-cache is WORSE than dropping the flush-cache plus all writes after the flush-cache. The problem that causes loss of whole pools rather than loss of recently-written data isn't that you're writing too little. It's that you're dropping the barrier and misordering the writes. consequently you lose *everything you've ever written,* which is much worse than losing some recent writes, even a lot of them.
Who said dropping a flush-cache means dropping any subsequent writes, or misordering writes? If you're misordering writes isn't that a completely different problem? Even then, I don't see how it's worse than DROPPING a write. The data eventually gets to disk, and at that point in time, the disk is consistent. When dropping a write, the data never makes it to disk, ever. In the face of a power loss, of course these result in the same problem, but even without a power loss the drop of a write is "catastrophic". -frank _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
