DragonFly kernel List (threaded) for 2005-01
Re: Description of the Journaling topology
Nikita Danilov <nikita@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
Solaris ZFS doesn't use journalling or anything similar.
You can read some interesting information about it here:
And a few more things here:
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:
- 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
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.
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)