> > Well, ok, and in my limited knowhow... zfs set checksum=sha256 only > > covers user scribbled data [POSIX file metadata, file contents, directory > > structure, ZVOL blocks] and not necessarily any zfs filesystem internals. > > metadata is fletcher4 except for the uberblocks which are self-checksummed > using sha256.
Surely you're referring to 'metadata' as 'zfs filesystem internals', not 'user scribbled data', particularly here, stat(2) info [commonly called metadata]? > SHA256 is approximately 1/2 the speed of fletcher4, so the trade-off > does not consider only the checksum algorithm. For older machines, > the speed difference could be worse. Hah! Considering I get only 20MiB/s read and about half that on write, I'm used to the pain :) Of course different algos come with a price, ref: openssl speed. > > Yeah, I suppose a pipe to ssh has enough bits to catch things these days. > > Netcat might be different, ergo, at least f4 as already implemented. > > I'm interested in anecdotal evidence which suggests there is a > problem as it is currently designed. Thus far, I believe the reports > of send stream corruption on this forum have been attributed to > other things. An anti-anecdote of sorts... With all the petabytes I've stuffed over unchecked ethernet/wan I don't think I've ever run into a confirmed case of data error there. Whether netcat/rsh/ssh/ftp/etc, it was always bad hardware. Especially the crap $megabuck SAN I ended up proving bad by wrapping backups with aes, sha and pki. Before then, I simply wasn't watching anything closely. Though it never seemed that the layer0 [wire] through layer3 [ip] checksums would be all that strong compared to 128+ bits of real hash. I can't seem to find a bit eqivalency for fletcher4. Though I don't think that's quite the way I should be thinking f4 works. Oh well, this thread's baked. Thanks for zfs, it totally made my world better. _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
