Description of the Journaling topology

[Oliver Fromme]

Nikita Danilov <nikita at xxxxxxxxxxxxx> wrote:
 > [...]
 > Attempts to improve performance of journalling file systems in this
 > regard, mainly rotate around a cluster of (arguably very old) ideas
 > called variously "shadows" (in the data-base world), "phase trees"
 > (Tux2), and "wandering logs" (in reiser4). From little technical
 > information available on Solaris ZFS, it seems it also uses something
 > similar.

Solaris ZFS doesn't use journalling or anything similar.
You can read some interesting information about it here:

http://www.sun.com/software/solaris/10/ds/zfs.jsp

And a few more things here:

http://www.sun.com/2004-0914/feature/

I'd like to quote one of the more interesting paragraphs,
which presents one of the main ZFS features:

"Solaris ZFS avoids data corruption by keeping the data on
the disk selfconsistent at all times. It manages data using
transaction groups that employ copy-on-write technology to
write data to a new block on disk before changing the
pointers to the data and committing the write. Because the
file system is always consistent, time-consuming recovery
procedures such as fsck are not required if the system is
shut down in an unclean manner. Copy-on-write also enables
administrators to take consistent backups or roll data back
to a known point in time."

On the second URL, there's a list of ZFS features and
benefits which sound pretty cool:

[quote]
 - Dynamic striping across all devices to maximize throughput 
 - Copy-on-write design makes most disk writes sequential 
 - Multiple block sizes, automatically chosen to match workload 
 - Explicit I/O priority with deadline scheduling 
 - Globally optimal I/O sorting and aggregation 
 - Multiple independent prefetch streams with automatic length
      and stride detection 
 - Unlimited, instantaneous read/write snapshots 
 - Parallel, constant-time directory operations
[end quote]

Sorry for this off-topic stuff, but maybe DragonFly can
pick up some of the ideas (or achieve the same benefits
in different ways).  That would be really awesome.

Best regards
   Oliver

-- 
Oliver Fromme, Konrad-Celtis-Str. 72, 81369 Munich, Germany

``All that we see or seem is just a dream within a dream.''
(E. A. Poe)