29 Jun
2011
29 Jun
'11
5:04 a.m.
On Tue, Jun 28, 2011 at 9:07 PM, Gabriel M. Beddingfield
<gabrbedd(a)gmail.com> wrote:
On Tuesday, June 28, 2011 06:49:24 pm Christopher
Cherrett
wrote:
Here's the simplified concept of a journaling file system.
For each chunk of data that will be written to the disk, the
procedure is something like:
1. Add a log entry in the journal that you are going
to replace data at location A with data at
location B.
2. Write the data for location B.
3. Point the file system to location B instead of A.
4. Delete the log entry from the journal.
That is not how it is (usually) implemented.
- For
hard disk recording... use a NON-journaling
file system like ext2. (E.g. mounted as
/tmp or something.) This removes the overhead
of updating the journal for each transaction
to the disk. If you have a power failure during
a recording, you're pretty fsck'd no matter which
way you go... so the journal won't help you.
What type of performance hit does journalized file
systems take?
While this generally happens pretty fast... chances
are that
the journal, location A, and location B are in 3 totally
different locations. That means that the your disk will
seek each time. This lowers your throughput/bandwidth.
A good journalled file system should perform at least as well. The log
is written sequentially and the data pages usually need not be written
synchronously.
There are many huge variables, of course. Writing the log to a
different device can help a lot. Etc. etc.
When recording (i.e. large, sequential files) on a
non-
journaling file system... you simply do step 2. Over and
over. And you don't have to seek. This improves your write
performance. But since you're not journaling, an unexpected
power outage can result in a total filesystem corruption
(but it's usually just a localized filesystem corruption).
With that said, I've never had a problem recording on a
journaling filesystem... but the original question was "what
is the best?"
The only way to really answer any of these questions is with realistic
benchmark comparisons (not easy to do well).
--
joq
Does a non-journalized file system give you less
latency?
No. It give you more hard drive bandwidth and more CPU
headroom.
Your hard disk performance has nothing to do with audio
latency.