[ Thanks to Paul
Shread for this link. ]
“1. Checksums in Metadata for Data Integrity
“Data integrity is of paramount importance in ZFS, and is the
driver for many ZFS features.“The file system uses a 256-bit checksum, which is stored as
metadata separate from the data it relates to, when it writes
information to disk. Unlike a simple disk block checksum, this can
detect phantom writes, misdirected reads and writes, DMA parity
errors, driver bugs and accidental overwrites as well as
traditional “bit rot.”“2. Copy on Write
“ZFS ensures that data is always consistent on the disk using a
number of techniques, including copy-on-write. What this means is
that when data is changed it is not overwritten — it
is always written to a new block and checksummed before pointers to
the data are changed. The old data may be retained, creating
snapshots of the file system through time as changes are made. File
writes using ZFS are transactional — either
everything or nothing is written to disk.“3. Data Snapshots With Time Slider
“The latest version of OpenSolaris illustrates the power for
ZFS’s snapshot capability with a small graphical application called
TimeSlider. ZFS can be configured to take a snapshot of the file
system (or a section of it, such as just a user’s home folder) on a
regular basis — every 15 minutes, or every hour, and
so on. These snapshots are very small and efficient, as only the
deltas from the previous snapshot are stored.”