[mythtvnz] Drive throughput

[Stephen Worthington]

On Sat, 10 Apr 2010 20:45:08 +1200, you wrote:

>On Sat, 2010-04-10 at 20:36 +1200, Stephen Worthington wrote:
>> I would be a little wary of the "eco" and "green" type drives.  They
>> are actually 5400 rpm mostly, although they can run faster sometimes.
>> I have WD 1.5 Tbyte green drive and it has wildly varying performance
>> with Vista - I can not predict if a given file transfer will be very
>> slow or very fast.  It is supposed to speed up to 7200 rpm as
>> necessary, but sometimes it does not even when copying a
>> multi-gigabyte file.  And the base speed when running at 5400 is
>> annoyingly slow.
>
>I've got 4 WD Green drives and find them acceptably fast for storing
>media and handling multiple recordings etc.
>
>> My recordings partition is JFS (recommended), with everything else
>> ext3.  I do not recommend ext4 yet as it is much more liable to lose
>> data and get corrupted in emergency situations (such as power failure
>> or PC crash).
>
>I also use JFS and like it but I'm not sure your accusations on ext4 are
>valid, do you have a source for them. I've been using it on my desktop
>and laptop for a while with no issues.

From the horse's mouth.  I was looking at the changelist for the ext4
driver a few months ago, and the author was saying that the changes he
was doing were to make ext4 perform a bit more like ext3 when it gets
cut off by a crash or power failure.  He said that ext3 performing
well under those circumstances was pure fluke, not a design feature,
but that everyone had got so used to ext3 doing it well that when ext4
did not, he was forced to sacrifice a bit of performance in ext4 to
make it work better, but not as well as ext3.

So, in your use of ext4, how many times have you reset or powered of
an ext4 partition without it having been shut down properly first?
That is when the problems happen.  With ext3, if the partition is idle
for 10? seconds, it will flush everything to disk.  Apparently ext4
does (did?) not do that for performance reasons, and could get caught
with things left in RAM that never made it to disk.  Ext3 can too, but
it is quite rare due to the automatic flushing.  Leaving an ext4
partition idle for hours could still result in things not being
flushed and a power failure has (had?) a pretty good probability of
catching it in that sort of state.