4185 New hash algorithm support

@@ -270,7 +270,114 @@
 
 When the \fBmulti_vdev_crash_dump\fR feature is set to \fBenabled\fR,
 the administrator can use the \fBdumpadm\fR(1M) command to configure a
 dump device on a pool comprised of multiple vdevs.
 
+.RE
+
+.sp
+.ne 2
+.na
+\fB\fBsha512\fR\fR
+.ad
+.RS 4n
+.TS
+l l .
+GUID    org.illumos:sha512
+READ\-ONLY COMPATIBLE   no
+DEPENDENCIES    none
+.TE
+
+This feature enables the use of the SHA-512/256 truncated hash algorithm
+(FIPS 180-4) for checksum and dedup. The native 64-bit arithemtic of
+SHA-512 provides an approximate 50% performance boost over SHA-256 on
+64-bit hardware and is thus a good minimum-change replacement candidate
+for systems where hash performance is important, but these systems
+cannot for whatever reason utilize the faster \fBskein\fR and
+\fBedonr\fR algorithms.
+
+When the \fBsha512\fR feature is set to \fBenabled\fR, the administrator
+can turn on the \fBsha512\fR checksum on any dataset using the
+\fBzfs\fR(1M) command. Please note that doing so will immediately
+activate the \fBsha512\fR feature on the underlying pool (even before
+any data is written). Since this feature is not read-only compatible,
+this operation will render the pool unimportable on systems without
+support for the \fBsha512\fR feature. At the moment, this operation
+cannot be reversed. Booting off of pools utilizing SHA-512/256 is
+supported, provided that the appropriate GRUB stage2 module is
+installed.
+
+.RE
+
+.sp
+.ne 2
+.na
+\fB\fBskein\fR\fR
+.ad
+.RS 4n
+.TS
+l l .
+GUID    org.illumos:skein
+READ\-ONLY COMPATIBLE   no
+DEPENDENCIES    none
+.TE
+
+This feature enables the use of the Skein hash algorithm for checksum
+and dedup. Skein is a high-performance secure hash algorithm that was a
+finalist in the NIST SHA-3 competition. It provides a very high security
+margin and high performance on 64-bit hardware (80% faster than
+SHA-256). This implementation also utilizes the new salted checksumming
+functionality in ZFS, which means that the checksum is pre-seeded with a
+secret 256-bit random key (stored on the pool) before being fed the data
+block to be checksummed. Thus the produced checksums are unique to a
+given pool, preventing hash collision attacks on systems with dedup.
+
+When the \fBskein\fR feature is set to \fBenabled\fR, the administrator
+can turn on the \fBskein\fR checksum on any dataset using the
+\fBzfs\fR(1M) command. Please note that doing so will immediately
+activate the \fBskein\fR feature on the underlying pool (even before any
+data is written). Since this feature is not read-only compatible, this
+operation will render the pool unimportable on systems without support
+for the \fBskein\fR feature. At the moment, this operation cannot be
+reversed. Booting off of pools using \fBskein\fR is \fBNOT\fR supported
+-- any attempt to enable \fBskein\fR on a root pool will fail with an
+error.
+
+.RE
+
+.sp
+.ne 2
+.na
+\fB\fBedonr\fR\fR
+.ad
+.RS 4n
+.TS
+l l .
+GUID    org.illumos:edonr
+READ\-ONLY COMPATIBLE   no
+DEPENDENCIES    none
+.TE
+
+This feature enables the use of the Edon-R hash algorithm for checksum
+and dedup. Edon-R is a very high-performance hash algorithm that was part
+of the NIST SHA-3 competition. It provides extremely high hash
+performance (over 350% faster than SHA-256), but was not selected
+because of its unsuitability as a general purpose secure hash algorithm.
+This implementation utilizes the new salted checksumming functionality
+in ZFS, which means that the checksum is pre-seeded with a secret
+256-bit random key (stored on the pool) before being fed the data block
+to be checksummed. Thus the produced checksums are unique to a given
+pool, blocking hash collision attacks on systems with dedup.
+
+When the \fBedonr\fR feature is set to \fBenabled\fR, the administrator
+can turn on the \fBedonr\fR checksum on any dataset using the
+\fBzfs\fR(1M) command. Please note that doing so will immediately
+activate the \fBedonr\fR feature on the underlying pool (even before any
+data is written). Since this feature is not read-only compatible, this
+operation will render the pool unimportable on systems without support
+for the \fBedonr\fR feature. At the moment, this operation cannot be
+reversed. Booting off of pools using \fBedonr\fR is \fBNOT\fR supported
+-- any attempt to enable \fBedonr\fR on a root pool will fail with an
+error.
+
 .SH "SEE ALSO"
 \fBzpool\fR(1M)