[mythtv-users] XFS: options when running mkfs.xfs

[Michael T. Dean]

On 09/06/2007 02:32 PM, Nedim Cholich wrote:
> On 9/5/07, Michael T. Dean <mtdean at thirdcontact.com> wrote:
>   
>> On 09/05/2007 10:45 AM, John Goerzen wrote:
>> <snip>
>> Basically, I had 200GB of data on the disk that was severely
>> fragmented.  It took me 10 hours to read that data from the disk and
>> write it to another local disk (on another bus).  That means the average
>> read performance was at least 5.5MB/sec--far more than enough for the
>> max 19.39Mbps (2.4MB/sec) of my OTA ATSC recordings.  However, while
>> /most/ parts of most shows played perfectly well, there were sections
>> where the fragmentation caused read performance to drop to the point
>> that it would play 1 second, then pause for 5-10 seconds, then play 1
>> second.  Once I copied the data to another drive and moved it back, the
>> shows played perfectly, and without issue.
>> </snip>
> Now you got me worried. What tool and more importantly what metrics do you
> use to figure out if disk/io is having hard time? iostats?
>   

In truth, mythfrontend was the only tool I really used to find out that
I/O performance was lacking.  (Though once I saw the playback problems,
I did use filefrag to see how bad it was before I fixed it.)

> Since I just added dual hd receiver I'll most likely hit the SD/HD scenario
> in the near future.

Even that situation isn't usually an issue if you're constantly
recording both (i.e. if you have SDTV and HDTV mixed in thoroughly
around the hard drive).  I had gone from a nearly full disk with only
SDTV recordings of about 1.25GB/hr (and most were 30-minute shows that I
had been saving to watch the whole series at once) to recording only
HDTV recordings at 4-8.5GB/hr (and most were 1-hour shows).  Since I
like to watch shows in order (and "all at once"), I watched the SDTV
first--usually one or two hours of recordings per day--and deleted it. 
New HDTV recordings got put in place, filling up some of the small gaps
from the SDTV, and since there were no large gaps from HDTV, the new
files got severely fragmented.

That's the only time I've had issues due to fragmentation.

But, in general, I'd say don't worry about it until you actually
experience playback problems.  When you do, you could just fix the
"broken" file--copy it to another location (with more contiguous free
space) then flip-flop the names and delete the original (possibly
creating a link in the original recordings directory).  Or, you can
"defrag" the whole file system by copying everything to another file
system, then deleting the originals or reformatting the file system, and
moving the recordings back.  The hardest part is making sure you have
space elsewhere for temporary storage.  :)

Mike