[mythtv-users] ext4 mkfs largefile4 option

[Stephen Worthington]

On Thu, 07 Mar 2013 11:00:13 -0500, you wrote:

>On 3/7/2013 10:42, Stephen Worthington wrote:
>> On Thu, 07 Mar 2013 07:52:09 -0700, you wrote:
>>
>>> On 03/07/2013 02:07 AM, Stephen Worthington wrote:
>>>>
>>>> The recommended filesystem for a recordings partition is JFS or XFS:
>>>>
>>>>     http://www.mythtv.org/docs/mythtv-HOWTO-3.html
>>>>     (search for "Filesystems")
>>>>
>>>> I use JFS on my 3 Tbyte drives and am very happy with it.
>>>>
>>> but has the documentation been updated to reflect the fact that ext4 is
>>> available? I am currently using xfs, but the bench marks seem comparable:
>>>
>>> http://www.phoronix.com/scan.php?page=article&item=ext4_benchmarks&num=2
>>
>> No, the documentation does not appear to have been updated to
>> recognise the existence of ext4.  But the major problem with ext
>> filesystems and MythTV is with the time taken to do file deletes of
>> large files.  I do not think that has changed in ext4 - the benchmarks
>> on that page you refer to shows that.
>
>I don't see any benchmark related to file deletion on that article, and 
>in fact deletion of large files is a fairly atypical usage pattern. 
>Mythbuntu has defaulted to EXT4 for several years now, and I've not 
>heard any problems of people having to enable the 'slow deletes' option 
>in MythTV intended for EXT2/3.

The first benchmark on that page is "4 GB Random Delete".  It is
*slower* in EXT4 than in EXT3.  However, those benchmarks are pretty
old now (2008) - EXT4 may well have been significantly improved since
then.

I most certainly have heard of people complaining about recordings
being damaged when using EXT4.  On setting the "slow deletes" option,
those problems usually go away.  It is a common problem with people
installing MythTV for the first time.

Mythbuntu defaults to using EXT4 for the system partition - that may
be a good choice now, but see below.  But when you install Mythbuntu,
you are supposed to create one or more separate partitions for your
recordings, and those should not be EXT filesystems.

When EXT4 first came out, it was discovered that it has significantly
worse performance in situations were the PC is suddenly reset, powered
off or rebooted without being shut down first.  EXT3 has default
settings that make it flush things to disk every few seconds.  To get
increased performance, EXT4 did not do that, and not flushing made it
much more vulnerable to power failures than EXT3 - it frequently
resulted in corruptions in EXT4 partitions when EXT3 would not have
had that happen.  As a result of that, I have stuck with using EXT3
for my Mythbuntu system partitions.  That was also back in 2008, and
EXT4 may have been changed since to fix that problem, or it may be
fixed if you use different options for your EXT4 partition.  But as I
have not followed up on any developments in EXT4, I still prefer EXT3
for that reason.  I prefer my MythTV system to be as robust as
possible, and power failures do happen.  My MythTV system using an
EXT3 system partition and JFS recording partitions has no problems
with recovering after a power failure - I have never yet had any
corruption in the filesystems as a result of a power failure (although
any recording in progress at the time will obviously be damaged).